If you register your home as business premises there is a danger of becoming liable for Capital Gains Tax on any profit when you sell.
You would also have business rates to pay, the Council would expect you to apply for change of use and could easily refuse permission, and your deeds may prohibit it anyway.

Many Councils have by-laws where you have to register with their Trading Standards people before trading cars, and they can and will enforce the rules.

You are obliged to register as self-employed within a certain period (can't recall if it is 30 or 90 days, but it's certainly not as long as a year).