You mention your soil, so I'm assuming that your clematis is growing outdoors but I'm not sure that Bedfordshire can provide a climate comparable with Thailand, which might explain why the plant isn't doing very well.

Is it one of the evergreen types, like 'Early Sensation'? They don't need pruning at all, but are a bit tender so often don't do very well in colder areas. Could you pot it up and bring it into a conservatory?

I think the 'Thais' is a typo Urbanite and should read 'that's'

That would make sense MG. It is the curse of iPads - they think they know what we're thinking!
The Thai clematis has a striking flower - looks like an expensive chocolatier's creation.

So getting back to Rose's question... I think there's too much mystery built up about when to prune clematis - if you look at the three methods they come down to 'tidy up after flowering' ie remove deadheads and trim back any over-tangled/unwanted growth.
Pruning, generally, seems to be turned into a ritual by the experts to confuse the novices and if the Rules are just too much to follow then prune back one third won't kill the plant and will give you some flowers next year.

Our C montana is an absolute thug and received a very, very, serious pruning last year. It is just putting out new leaf buds from the old woody stems, won't look good this year but will a year from now.

I've always steered away from c.montana - though I admit to planting a Russian vine (mile-a-minute) at my last house. It served a purpose but I won't make that mistake again!

Thanks to all that gave their opinion about my Clematis!

Still not certain what to do with my early white Clematis?
Yes, it is an evergreen one & has been really beautiful in the last couple of years but now looks so sad! I've tried watering, feeding (& even talking to it??), to no avail!
Fingers crossed that it survives?
Rozz.

What are you feeding with and when? When and how do you water it? Do you mulch?
Do you have any idea of the variety (ie the name)?