Sharon Griffiths wonders whether some of the Gift Aid largesse given by the public purse would be better going elsewhere.

The trouble with Gift Aid is the queueing.

There you are, waiting to get into a stately home or gallery and there's a whole coachload of people in front of you having Gift Aid explained to them, then slowly spelling out their addresses or fumbling for specs and pens so they can fill in the forms.

Nor can you any longer double-park for a few seconds and just nip out and dump a bag in a charity shop. Again there are forms and stickers and paperwork, even for sons' old jackets and a bag of books…

Gift Aid is, of course, a brilliant scheme. Charities can claim back 25p in the pound from UK taxpayers. You've already paid tax on your hard-earned income, why should charities pay more?

When husband and sons did a series of sponsored walks for cancer research we encouraged people to give the money through Just Giving website rather than push tenners into their sweaty hands as that way the charity could get the tax back. If donors registered for Gift Aid, it more than made up for the charge that Just Giving makes. For small charities it can make a huge difference. And at least the men felt they weren't paying tax on their blisters, which cheered them on their way.

It's great to think that good causes are getting something back from the government. Gives us all a Robin Hood moment. Yes!

And yet…

For a start there's that weird system where places offer you two admission prices – and the Gift Aid one is bigger. This means if you make, say, a one pound donation on top of the standard admission price, the charity can claim tax back not just on your pound but the whole lot. Don't ask me why. It seems somehow a bit not right. But I'm just lost in the forest of tax laws – as are lots of very clever people with maths brains. Just look at the mess some of those BBC people have got into.

And while all charities are worthy, some are, well... worthier than others. And are any of them worthier than the NHS?

Many are huge businesses with all the laxity that can sneak into large organisations. Others occasionally lose sight of the aims with which they were founded and move sideways into politics – or strange campaigns that make little sense to most of us. (Yes, National Trust, I'm thinking of you and those lanyards at Felbrigg Hall.)

But they still get the tax relief. And every 25p they get from the government means 25p less for the NHS or the police or roads or the armed forces or all the other stuff that our taxes pay for. It might seem like money for nothing but it's money from a very stretched pot. And sometimes, just sometimes, I think the NHS needs it more.

Not every charity donor uses Gift Aid. New research this month by HM Revenue and Customs showed that around a third of donors don't bother. That means that charities are missing out on a potential £600 million a year.

So now the government in one of its Santa Claus moments has written to 50,000 charities reminding them of a scheme where you don't have to fill in forms for donations up to £20 – which should speed those queues up a bit.

But though I dutifully declare and sign, I'm still not 100% sure. Charities can do a lot of good with that £600 million. But so could the government.

Who needs it most?