As someone that's worked in a major kitchen retailer for the past 20+ years, some advice:
It's tempting to walk into a one-stop-shop like Wren/Wickes and get "a price" for the kitchen, appliances, worktops + installation on 5 years interest free credit.
It's the easy option, but you'll pay far more than you need to.
Get a cash price for furniture only, no appliances/worktops.
Get multiple quotes and ask companies to price-match.
Do your research on things like door thickness/materials and finishes, don't let companies price-match on products that aren't like-for-like just because they look the same in a brochure.
The difference between a kitchen with 16mm thick laminate wrapped chipboard white doors and one with a 22mm thick painted & lacquered MDF white doors can be £4000+.
If you need finance to fund the project; apply for a bank loan on a low interest rate rather than go for interest free credit. That may sound silly, but it will work out cheaper in the long run.
A 10k bank loan on ~4% interest over 5 years will cost you ~£1000.
Retailers pay credit companies to provide interest free credit offers and they will artificially increase the price of the kitchen to recoup that cost from you.
It's ~£1000 to your bank or ~£2000 to your kitchen retailer.
Avoid Wren & Tecaz like the absolute plague.
Avoid Howdens unless you -really- trust your fitter. (And never buy Lamona)
Don't fall for "big" discounts; (20% +) they're invariably based on massively inflated RRPs and have no reflection on the value for money of the actual product.
Don't fall for "wow" offers; (like free granite worktops), they're offered by companies that simply inflate the value of the kitchen furniture to offset the cost of the goods offered.
DIY Kitchens can be good value but factor in their delivery charges, returns and paint batch retention policies. Buy everything you need and nothing that you don't. It's worth a trip down to their showroom.
I hear some complaints on their deliveries; they're often slow, late, have shortages/damages and on some occasions just don't turn up 'til the following day but their product is, by most reports, good value and of sound construction.