We garden on heavy clay soil too and unfortunately there is no 'quick fix'. All you can do is keep adding and incorporating lots of compost and sand or fine gravel. After ten years of doing this, we have improved our soil enormously, but it does take years! The advantage of clay is that is usually very fertile. It depends to an extent what you want to grow, but for vegetable gardening I would dig in sand and compost and then keep the ground covered with mulch, which largely prevents the cracking and going solid in normal summers. Keep off the ground as much as possible in winter to avoid compacting it.
For flowers and shrubs, choose things which will tolerate heavy soils and keep the soil covered with a thick layer of mulch around the plants, such as grass cuttings or shredded bark.

My mum even buried an old fashioned wool flock mattress in her clay front garden! Anything to lighten it up a bit. Opinions are divided on sand - some say don't use builders sand as its too fine, others say it doesn't matter, so you could run tests and let us know which woks best!

Avoid builders' sand as it may have salt in it, from the seaside. Horticultural Sand is labelled as 'washed' - I lost a lot of Alpines setting up a trough, using the wrong sand, which was sold to me in a GC by the manager who didnt know gardening.
I have found Patio Roses love this type of clay soil. They need a big area, as throw out shoots 10 ' long ! With all the wet weather mine are also shooting from the centre as well.
They make a good show, cover a large area of ground, but need hoeing underneath (when its dry) to prevent weed growth.

Greenenergy, can you please clarify whether you still want a lawn there, and are just asking what you can do to improve the clay structure of the soil? Or whether you want to get rid of the lawn entirely and grow something else instead? Only your question, to me, suggests you merely want to improve the heaviness of the soil for your lawn, whether that be the existing lawn or a new one. If that's the case, there is something you can do with the existing lawn, if its not full of weeds and weed grasses and is generally good.

Thankyou all for your responses...

Dear Bamboo

You hit the nail on the head. I do intend to maintain a lawn there, there already exists a fairly decent covering of grass though there's also a lot of weeds which I'm slowly tackling.

The ground is uneven so my idea was to rotivate it which would enable me to more easily remove the weeds, mix top soil into it and level the ground and then perhaps lay fresh turf.

If there is indeed an easier solution I would certainly appriciate your input.

Regards

Well, I don't know about easier, but there is an option. It's what professional greenkeepers do and its called top dressing. For heavy soil, you need to make up a mix of 4 parts sand (washed or horticultural), 2 parts loam (not just topsoil) and 1 part peat (if you can get it). Fine grade sphagnum or moss peat is best. Mix the parts together, and riddle if you have lots of lumpy bits. Then scarify the lawn thoroughly, spike all over with a garden fork, inserting the tines vertically about every 9 inches to a foot apart (stand on it to get it right down, and remove the fork at more or less the same angle it went in at). Once you've done that, you apply your topdressing mix - you need to spread it all over the lawn, filling in hollows where there are any, and brushing or raking the rest in, particularly where the holes from your fork are. The object is to get the mixture down to the base of the blades, not leave it sitting on top of the grass, except in the low spots. Best done in September. You can apply seed to the lowspots which you've levelled out with the mixture, because the grass in those parts won't be visible.
The thing that bothers me about your own suggestion is this - topsoil, unless you buy top grade from a good quality supplier, is usually just heavy clay soil, and often motorway spoil, so you may end up buying in soil which is just as heavy as what you've got already, and worse, also has a fair amount of subsoil mixed in.
I bet this has put you off - I'm tired just thinking about doing it, lol

Thanks Bamboo...

There's an awful lot of big words there, but I think I sort of get the gist... I presume that I can get these things at all good garden centres?

Also is this a procedure that I have to repeat at regular intervals, or is it just a one off?

Not sure about the loam from garden centres, will check later on with a friend who is a green keeper to find out where they get it from and get back to you. The moss peat is usually available at garden centres, but best to phone first - these days its not at all politically correct to be using peat, so often at the garden centre its hidden away round the back not directly in public gaze even if they have it.
The more times you repeat the procedure, the better the results because over time, it improves the soil structure of the lawn, so doing it annually would be good, but may not be strictly necessary,you may find its improved after one or two procedures.
Sorry about the 'big words' - ask if you want clarification, lol
PS: I too had a large lawn on clay soil, and had the same troubles as you - but frankly, I didn't let it worry me, all I ever did was ordinary lawn maintenance in autumn (scarify, aerate by spiking and autumn feed, with 2 summer feeds). Seemed to help a bit, and we didn't walk on it in winter anyway, when it was wet, but depends if you want a 'perfect' lawn or not really.

I had the same problem, think Bamboo's p.s. advice is the best. Works over about 10 years. Although in hot summers my little lawn was baked. The dead grass grew again as soon as it rained. In the current wet summer its looking wonderful.

Hi Bamboo

Was you able to source the loam for me?

Thanks for all your advice.

Regards.

I had a word with my greenkeeping friend. He says you go to seed merchants or good nurseries, sometimes very large chains of garden centres, specially out of London, have it available - and that they should have a ready made topdressing mix, which would save you the effort of trying to mix it all yourself. Tell them its to lighten up heavy soil (he says) and they should be able to point you in the right direction for whichever one is best. Often its just a mix of sand and good topsoil rather than peat in the mix too, but you need a higher ratio sand one for your purposes. He did give me the name of a couple of suppliers he uses, but of course, they're in and around West London, and I've no clue where you are.
He also said that, if you could source some very good topsoil that wasn't clay, then taking up what's there and rotavating and adding the good stuff will do the trick - he reckons that might be more effective, but its entirely dependent on sourcing non clay topsoil.