If you are a non-taxpayer (ie earn below £12,500 for the current tax year) and your spouse is a basic rate taxpayer, you are able to transfer £1,250

There are many personal circumstances that require you to complete a tax return and it is your responsibility to register with HMRC for self-assessment should your circumstances change.

The simplest diversification is to have a lot of dice (investments), meaning any losses may be counteracted by the other investments.