I'm liking the vapour barrier theory, but I'm not sure it would work quite like that particularly in typical UK conditions. I think this is one of those 'Yes, but...' questions. Yes, a cheap waterproof will keep the rain from soaking your underlayers, but you will mostly likely suffer from some degree of condensation. The point where that happens depends on a lot of different things including the outside temperature, but also how hot you run generally and how hard you're working.

If you're someone who functions on the hot side and sweats a lot, you're going to stew pretty quickly in a cheap waterproof. You'll also stew in a more expensive one, but it'll take slightly longer.

Berghaus did an interesting test with guys from KLETS a few years ago when Paclite first appeared. They measured the humidity inside a Paclite jacket and plotted it against terrain. On climbs the humidity rose as the tester worked harder, on level ground and downhill, the humidity dropped again as the jacket cleared the moisture outwards, so as long as the uphill wasn't too sustained, the jacket coped. Actually being Paclite, I don't think it was quite that simple as the grey liner stuff acts as a hydrophylic layer and soaks moisture up faster than it can pass across the membrane, so it's effectively a buffering layer.

Anyway, the hotter you run, the more demands you'll put on the breathability of your clothing, so it's worth factoring that into the equation as well.

Some years ago I did the Fisherfield 6 munros, a fairly long day out in the north-west of Scotland. It wasn't supposed to rain, so I just took a Pete Bland fell-suit - no longer available - a jacket and pants made from totally unbreathable sil-nylon, but at 370gm very light. As it turned out, the weather hadn't read the weather forecast and it rained hard continuously, so I had to wear the unbreathable jacket and trousers all day. I was surprised how warm it was - I guess because no sweat could evaporate, no heat was lost through evaporation, and while I was moving it was nowhere near as bad as you might expect, once I got used to being wet - the wet was very warm, much warmer than sweating in a breathable type jacket.  I think all I will have had on underneath would have been a base layer. I've worn the suit on other occasions, although I would never choose to, because it just feels so claustrophobic. It would certainly keep you more than warm enough to run off a hill in bad rain with just shorts underneath. The trouble with not very breathable garments though is when you stop; all that sweat has robbed your layers of any insulating value, and now starts to conduct heat away from you fast, which is not so good.  As to true 'vapour-barriers' as I understand it you wear something entirely non-breathable right next to your skin, which then keeps sweat away from your insulation, and then another non-breathable layer on top of your insulation layer. I've tried that with a couple of bin bags, and can feel how it would work.

I think that what I was really attemping to say is that no matter be it a cheap and cheerful Regatta option, or a much more expensive Gore-Tex, I eventually found I got wet wearing either in periods of heavy driving rain, especially where shelter from wind or rain could not be found over exposed ground. Because of this I do not feel it actually worth spending out hundreds of quid on any single expensive waterproof garment as such!Hopefully, together here, we have given you a whole base of different clothing options to look at, and indeed to think about there though Ben!

Excellent Ben, glad to hear we could be of help to you! I remain really much impressed, I must quickly say, with your just three first good posts so far here on this great OM forum; in that you have packed much more into them than most newbies do coming on the forum in very many more posts, I reckon-and so too more than I certainly did on my first posts on here, definitely!Good going, and glad to have you aboard here now too! I look forward to having a natter with you again on more outdoors topics indeed soon I do hope!

Thanks again. The resources available on the internet now for a newbie, and especially this site, are excellent. Gives more confidence buying kit.