New wheel set.

check out bikehubstore.com

Santa delivered me a pair of lightweight hubs, kinlin xr19w rims and sapim laser spokes and brass nipples. Weighs in at 1340g for 20/28

£40 to build em. Whole lot for under £300.

I had a set of kinlin 200 rims last year that i used on the Marmotte. Having light wheels will improve your speed going up hill just be careful to check on weight restrictions

Hate to bore you but I vote pro lite braccianos too. Also done several thousand miles on them. Commuting through all weathers on London's potholed roads. Roll like a dream.

Pro lite Braccianos are real bargain have used mine for training, racing and tour of Flanders sportive and been very impressed

Another vote for the Braccianos here.

Mine have done several thousand miles and are still great. I traded up from Campagnolo Vento's and found the difference remarkable, particularly going uphill.

They also roll down hill very well too. The only wheelset I've met in the same universe ie under £500 that has freewheeled faster than mine was running on brand new Chris King hubs. (using a very unscientific riding side by side testing method)

Pro lite Braccianos are a good choice; you won't get lighter at your price point. Roll well to.

Pro Lite Braccianos - under 1500g and within your price range (you can usually find them discounted to under £250). I love mine - they've proved to be bomb proof on London streets despite the relatively light weight. Keep your old wheels for winter training or the turbo - you'd end up spending at least £100 on parts to rebuild the hubs with new rims and spokes - if you're going to do that you might as well get new lighter hubs as well.

If your hubs are still in good nick, why not have a lighter rim built onto them? Rims are around the £40 each mark, spokes another £25 or so and allow another £40 for the build. You'll have a lighter set of wheels and be well in budget.

Handbuilts from planet X reduced and will be further discounted on the 28th (I think).

There's a variety of options there too to suit budget

Fulcrum 5 at about £180