@awomaninsane - try to stretch your budget if you can. £260 is not a lot for the number of components on the bike and the job you are expecting them to do. If you can spend more, you won't be wanting a better bike or upgrading bits quite so quickly.
Decathlon's great, if you're not a brand name snob there's plenty of decent kit in there.I want to have a look at some point, it will be my first visit to a Decathlon.
A higher end shop nearby is Team Cycles, which I think has only been open for a couple of years.
Go Outdoors at Portrack Lane in Stockton has a banner about an extended cycling department, so it looks like they are pushing that side of the business.
http://www.teamcycles.com/
Decathlon's great, if you're not a brand name snob there's plenty of decent kit in there.
I've got both running and cycling clothing from there that works just as well as more expensive stuff.
I'd imagine as with all chains peoples impressions of them will be based on the individuals in the particular branch they use, I'm lucky having the Bolton and Stockport branches close by.
Not sure how far you are from Newcastle.
Edinburgh Bike do test rides - I think they may keep your credit card as a hostageNot sure how far you are from Newcastle. Edinburgh are a good outfit and may be able to let you have a test ride if you ring to check they have one in stock.
I'm 5'5'' too and normally ride a 50 or a 52.