VAT increase = increase to lesson charges?

I was going to say the same as dc88, but s/he got there first! A lot of costs and charges in many sectors undergo an annual increase in January - train fares are one which comes to mind, as well as of course the VAT! So in a sense, people almost tend to expect that charges will increase at this time of year and it's a good time to implement this. I agree, simply inform parents that your rates will go up to £20 per hour as of next month - you could explain it's to take account of increased petrol charges etc if you want to, but certainly I don't think you should be apologetic about it. You are offering a professional service after all and having to travel to them. Personally, I also think that £20 per hour for KS2 tuition is about right and not extortionate by any means (it's what I charge and £25 for GCSE). You are a whole year more experienced as a tutor now too, so I think it's a justifiable increase.

 

Do the maths and the VAT will cost you about £150 to £200 a year extra. You should be claiming petrol costs as mileage in your tax return so you can't really charge extra 40p / mile to a parent and then claim 40p / mile on your taxes.
You also don't charge VAT on tuition I presume. Of course, you could increase your rates to £21 a session (but that is a pain of a number in cash)