Somebody is using my address to apply for financial services

[LordTrash]

I've had 3 letters in the last 3 weeks addressed to the same total stranger - all for financial type services (today's is from FluxDirect, an insurance company).

I've been sending them back with 'Unknown at this address' but I'm worried that our credit score might be at risk if somebody is constantly applying for stuff using our address. What can I do to avoid this?

You don't need to worry. Your credit rating relates to you personally, not to your address. None of this will appear on your record.