Google UK sites only

I'm fed up with putting something into search, finding a site which has just what I'm looking to order online and discovering it is an American site. How can I ensure that the sites that they show me are just UK sites. I have googled this and still can't understand what they are telling me to do to achieve this - I seem to have some choices missing from my google homepage.

Can someone help please in 'dummies' language - thanks

I search using and I find that if I search , say for Motor parts then I will get everything incl US suppliers, if I add U.K ie 'Motor parts UK' then only UK suppliers are listed

So if you are searching for '500GB hard drive U.K' you should be OK! but below the line you are likely to get 'similar' search results, in my case from French suppliers,