Ethics and Gift Aid

I appreciate this is a slightly random topic but I have been thinking recently about the ethics of Gift Aid. Gift Aid seems to be a wonderful scheme which has benefited many charities, not least the church. It is available to all UK tax payers and means that by making a simple declaration you are able to add £0.25 to every pound you give to a charity.  This £0.25 is claimed by the charity from the government - and each £0.25 comes from the tax you have already paid.  So it is a way of re-allocating the tax you have paid to a charity of your choice.

So far so good.  But unless I have missed the point (and will be happy for someone to put me out of my ignorance) this means that every time I Gift Aid a donation, I am in fact taking money out of the tax I have paid to support essential services, and putting it somewhere else.  I know this seems churlish, but I'm not entirely sure that this is OK.  If my tax pounds are needed to support the NHS, schools etc. is it really ethical for me to choose to opt out of part of that essential payment by re-allocating it to my chosen charity?

I suppose for those who understand this area better than I there are many mitigating factors. I would be happy to be enlightened.