Less than £100 will get you bins that are very good. Nearly all bins these days are excellent for the money, and the improvements as you spend more can be surprisingly small (or hard to see until you know what to look for).
I'd consider a pair of 8x32. They're a good compromise between the more popular 8x42 and the little fold-up pocket types. 8x42 are quite chunky feeling in the hand and aren't really pocket sized - best used with the case over the shoulder if you want to put them away (or with a satchel or the like). Weight is usually 700-800 grams. 8x32 is a bit shorter, the tubes are a smaller diameter, and they'll generally weigh around 200g less. Size-wise, they're small enough to go easily into most jacket pockets. In use, they feel noticeably lighter and more compact than 8x42, but still handle well - decent comfy grip that feels secure and stable. The 8x21 types are very ergonomically compromised in comparison.
There are loads to choose from, and I have limited experience with 8x32s. I started with a pair of Barr & Stroud Sierra 8x42, and they're excellent for the current price of around £80. I haven't tried the 8x32 version, but I'd be very tempted if I was after that size of bin. I did look through the RSPB Puffin model in 8x32 (£55), and was not so impressed. Some of the dearer RSPB models were more like the Sierras in terms of optical quality, but tended to cost more (maybe £120 or so).
In my searches, I found three makes/models that had suspiciously similar specs, not to mention designs of eyecup, focus wheel and dioptre adjustment. They're all made in China (just about every bin under £500 is made in China), and my feeling was that the various brands were buying a particular model and spec from the same factory, and getting their own design of rubber armouring added. The three that look to be the same are...
Barr & Stroud Sierra
Hawke Nature Trek
Celestron Nature DX
These three get consistently good reviews, both in terms of punters commenting on the likes of Amazon, and in binocular tests by people that presumably know what they're talking about (like "best binocular under $200" round-up kind of thing). Not sure how common the Celestrons are in the UK. The Hawkes are probably more common than the Barr & Strouds, and both of them should be readily available from a variety of sources. Worth shopping around a bit - you should find them in 8x32 for about £70.
