Hi, I need to rank for a term like: find design patterns But finddesignpatterns.co.uk is taken. Will it make much difference to SEO if I just purchase: ifinddesignpatterns.co.uk Or finddesignpatternsnow.co.uk Etc, etc, etc..
Many sites rank #1 for heavily competitive keywords and don't even have one keyword in the domain name. It does help, but is not a major deciding factor in cases that involve heavily searched keywords and phrases. I would suggest making something you can brand and have easy to remember and still related to the subject.
As ssandecki said, keywords in domain do help, but not to a point to lead to you #1 spot. In any case, what I would advice (on which domain to pick) is the one when you read from a user perspective and makes sense to you, is easy to remember and calls for action.
Interesting One thing I did notice is that the org.uk is available, not sure they rank so well though :S
I would try to use a *.com or *.org, unless you want to directly target UK customers only, then go with co.uk