I have to start with disclaimers.
- I'm not familiar with availability of various makes/models in the UK or their pricing. I will quote US prices in dollars.
- I don't know your observing preferences or how a particular binocular will suit you, so my thoughts represent my preferences and needs.
- When comparing different sized objectives, different magnification, or other physical attributes, including field of view, I assume we are comparing binoculars of similar optical quality.
- Binoculars in the price range you mention go on sale here, and there are factory rebates as well. If a model is being phased out, this can sometimes double or even triple your purchasing power relative to list price.
First I want to echo what JoeRawles said. Consider what you like or dislike about your current binocular and then bring them with you to a shop, or a birding fair where you can compare a number of models side-by-side. Comfort in hand and comfort of view is of paramount importance and it varies from person to person.
I prefer 8x magnification to 10x and higher because I just can't hold the higher magnification steady enough to get much more detail. Many people prefer 10x. I also like an 8x32 binoculars because they are compact, lighter weight, and lower in price compared to a similar 8x42. At 10x I would definitely recommend a 42mm objective for general use. The added size and weight of a 10x42 will make it easier to hold steady, and the larger exit pupil will make it more comfortable to use. Even at 8x, a 42mm objective has advantages in comfort of eye placement and added light grasp under low light conditions. Also, it seems like mid-range 42mm binoculars tend to be better baffled and produce less in the way of glare. However, my experience is that a good 8x32 really holds its own under the vast majority of lighting conditions.
There are two 8x32 binoculars that are often recommended here as good performers at a moderate price and I own both. A year ago I purchased the Sightron II 8x32 for $179 and a couple months ago I purchased a Cabela's Guide 8x32 (said to be optically identical to the Leupold Mojave BX3 8x32) for $149. I prefer the Cabela's Guide, but both are very good, and I use both of them regularly. I have tried a number of other 8x32 binoculars and have not found any that I preferred to these two until I was up in the $400-$500 range. BTW, one very nice binocular in that higher price range was the Opticron Traveler 8x32 ED.
My experience and the sense I get from reading reviews here, is that there are sweet spots where you get quite good value. I expect it is partly the marketplace and also that more sophisticated designs/implementation become available at higher prices. The two 8x32 binoculars I mentioned at just under $200 are a huge step up from anything less expensive unless you are getting a known quantity on close out. The next break point seems to be around $500-$600, and then at the $1,000 point there is another very noticeable step up. I have looked through the $2,000-$3,000 binoculars briefly, but have never owned one and can't comment on the improvement at that level.
Someone else will have to help with 10x42 in particular and 42mm binoculars in general in your price range.
