What size is the pot within the cache pot and are you making sure the tree isn't sitting in standing water?

Make sure your pot isn't too small for the lemon tree. Just like Moon_grower suggests, I think you should check for wet feet. You should also rotate the pot and make sure there is enough ventilation in the room. If the leaves are too damaged, you should get rid of them before they infect the branches. Maybe this guide here will help you:
http://gardening.answers.com/fruits-and-vegetables/how-to-grow-your-own-citrus-tree

I also agree with Moon growe. Consider repotting it to a larger pot. It may be root bound and depleted all the nutrients in the soil. Over watering will cause the leaves to yellow and drop off. The roots must be able to breathe.

We have had problems too with ours, tried the repotting, or not repotting.....it does best outside in the fresh air but obviously can't stay out!....

Thanks all of you !
Moon grower, Bathgate and Jane, I have repotted my lemon tree not that long ago and is not pot bound at all ! The first thing I did was to check if it was too wet and it wasn't ! If anything , it was more on the dry side !
I never ever stand it in water ! I water it well and let it drain off outside, if its a good day, or into a tray if its not ! When the tray is full of water I tip it out !
Last year I had no problems with my tree at all !
The conservatory is always well ventilated Amy and once when I put it outside, it wasn't at all happy !
Its a mystery !
I will look at that link Jane and see if I can find anything out from that !
Once again...Thank you

What are you feeding it with, Rose? It looks deficient in magnesium, maybe also nitrogen, since growth is stalled.

I feed it with a special citrus feed Tugbrethi .

Just wondering if it got scorched - the branch nearest the window looks worst affected.

It does look to be short of magnesium, but if its going short of water, that would prevent uptake even if its present in the compost or your fertiliser. And it looks to me like its been short of water...

I don't think its been scorched Steragram ! Our conservatory faces north ! Thanks anyway !
Its neither been too wet or too dry Bamboo, but I went on the link Jane sent me and one of the main things it said , was that it was better to be too dry than too wet !
Thank you for your input !

Oh dear. Perhaps try Epsom Salts then.

http://www.gardeningknowhow.com/edible/fruits/citrus/curling-citrus-leaves.htm

Might be of interest Bendipa...

I forgot to say I doubt its short of potassium because you've been feeding - but again, if insufficient water is/was available, potassium uptake would be affected.

Its not Red Spider Mite is it Rose? I remember my first lemon tree failed because of them and they are really hard to get rid of once established. Most bug sprays don't bother them either. And if its been indoors it will be more vulnerable. How I hate those little red devils!

I haven't seen the usual cobwebs that you get Karen, but what I did find once was a weird brown long hard backed insect surrounded by a very thick cobweb ! I squashed it and wiped this bit of cobweb off, but it wasn't anything like the red spider mite cobwebs you get !

Thank you Bamboo for all your suggestions !

My apologies Rose - I was obviously having a more than slightly senior moment - I put Bendipa when I meant Rose!

Ugh...sounds horrid. No idea what that would have been. Maybe a chrysalis?

Is that food a soluable powder, Rose, or a dry granule? Do you know the N-P-K numbers? Does it have directions for containers? Golly, I'm being a nosy parker!
Still, no sign of spider mite, that I can see, and that website on curling citrus leaves doesn't cover the type of curling that is showing on the photo. I have mainly seen that on citrus trees with serious nutrient deficiencies, especially nitrogen, and/or trees that have been too cold in the growing season.

Thats okay bamboo ! This is beginning to be something of a mystery !
I don't know what it was Karen ! I didn't even realise it was an insect until all this gpooey stuff came over my fingers !
Ugh!
Its a special lemon tree fertiliser Tugbrethi , so should have the right nutrients ! Its also a soluble one !
Thanks anyway !

A soluble fertilizer needs to be applied about every 3rd or 4th watering. For watering, I would let the top cm of compost dry out before watering again, then drench the pot thoroughly, being sure to empty...hmm, I just realized that I'm not seeing a drainage saucer, and on a nice floor, too. Rose, does that pot have a drainage hole?

We have a similar problem Rose and have tried everything thsts been suggested here, even purchasing special summer and winter feeds.....

One thing I do wonder about is lack of humidity.....standing on stones didn't help......
in hot countries how do the citrus groves manage?....

Yes...I do all that Tugbrethi, although I think I perhaps should feed more than I do ! The instructions say once a week . I have an inner pot in this one and both have good drainage holes. On a good day I water it outside, but other days I have a huge drainage saucer and when it has all drained through, empty it out !
Pamg, I really must apologise, I've just noticed that I have been calling you Amy ! Its strange Pam, as last year I had no problems at all ! Maybe I'm trying too hard ! Last year I think I only watered when I remembered ...could have gone weeks and I also used a summer granule fertilizer which you only applied once !

I quite like the name Amy ?
gran always confused pam & pat my cousins ........

i know what you mean about trying too hard, probably they really just want the mediterranean climate .....

I always do the same with our grandaughters Pam !
The lemon tree is now outside in disgrace ! lol
I found red spider mite on it today, as if its not enough trouble ! I sprayed it well and am leaving it out for a few days, so it will probably sulk after being in a lovely warm conservatory !

It probably needs to be outdoors anyway at this time of year, day and night! They 'do' get frosts where citrus fruit grow naturally and I suspect all our 'wussing' of them does not do them any good!

My view is if I can't grow it outdoors I won't grow it at all! I know tho is a personal thing but I just can't see the point in growing something that needs so much care and attention.

Indoors, Rose, A citrus tree probably could go 2-3 weeks between soakings. Depending on the mixing instructions, once a week is usually intended for outside growing in areas like mine, where we need to water practically every day! Other than that, I have no idea what your plant's issues are. It's a puzzle to me! :/

I know what you mean Mg.......in the garden we grow to suit the conditions, citrus was a big hope, and the lemons were lovely ?

I think you are right Moongrower as last year I didn't worry about it and it never had one problem !
Tugbrethi, I only watered it about once a month in the conservatory last year, so maybe I have been too fussy this year , especially when I counted 22 lemons on it !

There you go... less attention and it will probably do fine :)

Trouble is now Moongrower...it hasn't stopped raining since it went outside ! Its definitely going to be sulking now !

So am I with all this rain ?

Usually, we desert dwellers dance in the rain, but not so much this past week: lots of flooding and storm damage, here.

Weird weather all over then Tugbrethi !

Whats this on the news about weather in the Pacific? I'vebeen away and missed the details.....