Just for clarity, in the UK police CANNOT just enter your home for the hell of it without a warrant, unless they're in pursuit of someone, or you invite them in. They MUST tell you who they are (including providing their warrant card or ID number), what they're expecting to search for and why they're expecting to search for it. The cannot search your person without a specific power to search, and it is illegal for them to ask you to "consent to a search". You have every right to tell them to sod off (politely of course, otherwise they'll probably arrest you for disturbing the peace while they're at it, at which point they do have the right to search you but not your property)
For a general overview see
This WikiPedia article
Disclaimer: I'm not a lawyer, do your own research and/or consult a legal professional if you're unsure.