I know many parents reading that question will instantly know what I’m talking about.

It’s that little phrase that schools put on the end of any letter where they are asking us to pay cash to the school. It might be for a school trip, a workshop or something else.

Most parents find the money to pay for their child to take part. Some cannot afford to pay and some, seeing the word ‘voluntary’, just don’t bother. So what is acceptable and what is not?

This is an interesting question as parents respond to different requests for money in different ways.

In the state sector we expect to get education free for our children. We do, of course, pay for this through our taxes. However, in the 15 years I’ve had children in state schools, the annual cost of paying for extra things, on top of uniform and school meals, has consistently risen.

But in state schools does ‘voluntary’ actually mean ‘voluntary’? In January, a school in Bath wrote to its parents asking them to pay up to £30 a month for its school fund to keep up its activities. Some parents were outraged and this was locally reported.

There have also been other cases at different schools of schools asking for a £15 donation towards the cost of running a sixth form centre and, apparently, those who didn’t pay up were denied certain privileges.

I’ve raised this issue as it’s come home to me just before the children broke up for the Easter break.

My son’s primary school has always had swimming lessons for Years 1 to 4.

However, the school may soon have to cancel this ‘luxury’ extra. That’s because, this year, a significant proportion of parents have not paid up. According to the school, for the term which has just finished, of the 164 children eligible to go, only 107 payments were made. So 57 families paid nothing.

Their children still went swimming and – because it’s not allowed – the school is not able to ask parents to pay extra to cover those who don’t pay. The school will have had to subsidise the cost of swimming to the tune of £5,000 if this situation doesn’t improve over the summer term. The school has made it clear this is unsustainable.

Is this right? Or should parents be able to choose whether to pay or not?

It is an emotive issue and one that is not going to go away.

I just hope, in this case, that those parents who can afford to pay, do so. However, one thing is clear, voluntary doesn’t actually mean voluntary.