Not to sound biased or anything, but personally, if I were you Halo, I'd try to get some old Canadian army od's. They're absolutely amazing for the bush, and as our Forces don't use Olive Drab anymore, there is literally tons of clothing (a lot of it brand new) just waiting to be sold. I have a pair and I'm planning on getting another for hot weather bush wear.
The secret with these pants is the weave. It's a very loose "aertex" as I think you Brits call it. It has also has three layers. The middle layer is nylon and it's backed on both sides by 100% cotton. The cotton keeps you cool and comfortable, and the nylon aids in durability and makes them dry very quickly. So quickly infact, that I've seen guys with soaking wet OD's rub them with the palms of their hands and in minutes, they're dry.
They also have our famous "tape" slotted buttons, butt pockets, hip pockets and map size cargo pockets on the legs with drains in the bottom. Oh and the leg's have a rolled up gaiter inside of them that you tuck into your boots or socks to stop rocks and dirt getting into them. They also come with a cotton lace to blouse them.
Here's a URL for you:
http://aasurplus.ca/store/product_info.php?cPath=24_135&products_id=155
Ignore the fact that the site says they're 100% cotton, because they're actually 50/50. You'd probably need a size 7040 or something along those lines. And since you're in the UK, the exchange rate would no doubt work well for you!
Cheers,
Adam
