Another hi from up the road, i am near Burton upon trent
Kind of a cross post but as you said you tend to be looking at bikes at the lower end of the cycling price bracket, there is nothing wrong with "cheaper " bikes if it does the job you want it for and avoid what is called a BSO (bike shaped object) which are the bikes sold at places like argos and supermarkets and the apollo range at
Halfords used to get a lot of stick as they tend to either have substandard parts or are put together badly.
I use a second hand carrera TDF for commuting which cost me just over £100, and my "best " bike is only £400 brand new in the shops , but i got it for £250 off a private add in a cycle forum .If you know what to look for and can shop around you can get cracking bargains.
If you want to learn more about bike maintenance then look at this website as it is very handy !
http://bicycletutor.com/
When you have the tools you can save a lot of money, i recently replaced the gears + chain on my bike and it cost me £30 for the parts and maybe 20 minutes for the whole job, i would not even like to think how much a bike shop would charge me for it .