How much is a 0.1 carat diamond worth in sterling pounds?

A diamond is 'worth' whatever someone will pay you for it, in whichever currency is being used for the transaction.

The smallest diamond available for this kind of comparative purchase today, online is a .25 carat diamond, larger than your .10 carat query. You can buy this diamond today 11Sept26 on Blue Nile and pay between US$232 or 139.50 BPS and US$516 or 332.52 BPS, depending on the cut, clarity, colour and carat weight of the diamond.