No tax deduction, but a tax credit. The divi is paid at the stated rate, it is assumed that the company has paid tax on profits so they give you a tax credit of 10% (ish, you will see on the voucher that the tax credit is 10% of the total, divi paid+ tax credit).
The tax credit in this case will be 500*.242/9. Or �13.44
You put it on a self assessment form but it makes no difference as the tax is already paid and you cannot claim it back if you don't pay basic rate tax. If you pay higher rate I think they tax it some more.