On 29 August I'm jumping into the canals of Copenhagen to swim 2km in open water (Trygfonden Copenhagen Swim). It may not sound like much, but I am no athlete and have never been keen on endurance sports – never mind open-water swimming. There will be no lane ropes or pool walls to grab onto, just me, a couple of friends, some other enthusiastic swimmers (who are likely a lot more capable than me) and some very chilly water.

I'm raising money for Swiss Cottage School Charity, which is a state-funded special school for children and young people with complex special educational needs and disabilities. The core budget from central government covers the school's most vital resource - its expert staff - and basic equipment. But as the school itself puts it: for a student population with complex needs, "basic" is not enough. The specialist technology, sensory resources and the highly personalised education that allow pupils to reach their full potential and truly thrive fall entirely outside that funding.

The charity exists to fill that gap: funding specialist equipment, learning opportunities, and experiences that promote real social inclusion of pupils. This includes experiences such as community outings and residential trips which parents of children in mainstream schools simply take for granted. For young people with complex needs such activities cost far more than a standard school trip and well beyond what most families could cover, even if they wanted to. Without the support of the charity, these experiences just don't happen.

My son Alex is soon entering his final year at Swiss Cottage. He recently came back from a five-day residential trip with his class. He absolutely loved it. His independence increased, he tried new experiences, he had a lot of fun away from his parents and was very proud of himself in a way that is genuinely hard to put into words. That once-in-a-lifetime trip was made possible by the charity. It would not have happened otherwise. For a moment in time he got the help he needed to experience what other 18-year-olds do – going on a trip without his parents. An important step in growing up and becoming more independent.

Think about a school memory that stayed with you: Taking part in a dance performance, playing music with others, feeling a sense of achievement and doing something that made you grow. That's what this money is for.

Alex moves on next year. This swim is my way of paying it forward so children coming up behind him get the same chances he had.

Any donation, however small, helps directly.

I'll report back from the finish line. Assuming I make it out of the harbour.