Kelty have a UK dealer listed on their web site at www.kelty.com - MAN O' LEISURE 01395 443789, but they don't have a high profile in the UK, in fact I was kind of surprised to find they have a presence here at all...
There are plenty of other good tents around however. Hilleberg are developing a really positive reputation - www. hilleberg.com - for making excellent lightweight tents in Sweden. I also really like the New Zealand brand MacPac and brands like Terra Nova have a proven record.
Sleeping bags? The two top specialist UK makes are RAB and Mountain Equipment. For warmth to weight ratio, down is best, but it's more expensive and needs more care, particularly keeping it dry. Synthetic fillings are improving all the time and for a summer bag, will still be pretty light and compact and cheaper too. A 2/3 season bag should take you into autumn and late Spring which with our luck'll be just the same as the UK summer anyway... Get one with a zip so you can vent and stay cool if it's really warm.
You'll also need some sort of sleeping mat as lying direct on the ground is pretty cold and uncomfortable. The ultimate is a Therm-a-Rest-type inflatable mat, but again they're expensive and you can buy a perfectly adequate foam mat for a lot less. It won't be as comfortable, but then it won't leak air either and will be lighter too.
For cooking, I'd stick with gas as it's so simple and easy to use, though not always cheap. The GoGas stoves we've tested have worked well,but whatever brand you pick, the most stable design is one of the tripod-type alpine stoves. The ones that mount on top of the gas canister are light, but can get unstable.
It makes sense to keep the weight down, but you'll soon discover that light, high quality kit does tend to be more expensive. Other tips, well, there's obvious stuff like practicing putting the tent up before you use it for real - it'll save epic messing around in the dark, but then again, that's half the fun of it...