what happenes if you get caught bunking off school lessons in the UK?

It depends on your school. I mean, there's no law that states, "If you miss a lesson you get detention." At least, I think so. I'm pretty sure it varies with the schools.

In the UK skipping school, being truant, or playing hooky may be a criminal offense. Headteachers, education welfare officers (also known as education social workers), whose job is to make sure that children attend school, and police officers may decide to give you penalty notices of £50 to £100 if your child regularly misses school and you have not taken action or asked for help. If you don’t pay a penalty notice you’ll be prosecuted.

Prosecution can result in a fine of up to £2,500, a jail sentence of up to three months or a community sentence. Good luck. I was a college professor of education at four universities in the U.S.

mum and dad could get fined