Why are my lavender flowers white?

How interesting. I have no idea, but am hoping someone else does - I'll be following this question with great interest, though this isn't much use to you!

there are several cultivars of this ranging from white, pink and blue but never heard of a plant reverting to one of its parents. You could try contacting a specialist lavender nursey for advice. Im sure they would be able to help.

PS if you cant find anything locally try Downderry nursery in the UK

Try Isle of Wight Lavender, they are experts and may be able to give you help. http://www.lavender.co.uk/
There are white varieties, but I'm not sure why your established plant has suddenly decided to have a change!!