I assume you are talking about the VAT applies to digital books, and hence we pay extra 20% compared with "real" books which under the UK are VAT exempt.
Actually, in Denmark, VAT (MOMS) is applied on real books as well as digital book at a higher rate of 25%.
Rates vary quite a bit in different countries on VAT rates on books as shown in following
http://www.vatlive.com/vat-rates/eur.../eu-vat-rates/
What is interesting is that some member states also have reduced VAT rates on e-books.
So, if an individual member state can reduce the VAT on e-books, then presumably so can the UK. So is the EU really the culprit as you imply, or is it the UK?
I suspect the UK has not sought an exemption, as when e-books started, the volume of sales was too small to be worth making an issue over.
Of course sales have greatly expanded, but I still doubt the UK will do anything as the extra VAT is a "nice little earner", and in reality, even with VAT, e-books are cheaper than "real books" (for same book) as far as I can tell.
The problem with this type of petition, it is not easy to put a strong case for change - take fuel taxes for example, it can make the difference between a firm surviving or not, and hence petitions have a strong meaning. I seriously doubt e-book sales are affected enough by VAT to put budding writers out of work
To simply petition based on the argument "I want to pay less" can be applied to anything with VAT e.g. why do we pay 20% on adult shoes etc.
Regrettably, I think your campaign is doomed to failure, as I doubt you can provide an emotive enough justification to make the UK government agree to make changes. Of course, I could be wrong - good luck anyway.