The headmaster of one of Britain's top public schools has warned pupils they could be expelled or receive a negative university reference if they form romantic relationships with their peers.

Toby Belfield, principal of Ruthin School in Denbighshire, north Wales, wrote an email to students highlighting that pupils engaged in a relationship were "at danger of academically underachieving".

"Parents choose Ruthin School because it is a top-ranking academic institution," he wrote.

"In my experience, students who are in a relationship, whilst at school, are at danger of academically underachieving.

"Therefore, if they devote their time to their studies, rather than the emotional turmoil connected with teenage romance, they will achieve higher grades and go to better universities.

"This is the primary objective of the school - to enable them to fulfil their academic potential and go to the best universities in the world. "

According to The Times, in the email addressed to the school's staff Belfield wrote: "Relationships can start at university — not at Ruthin School."

"I strongly disapprove of any boyfriend/girlfriend relationships — and it will always affect any university reference I write [. . .] I will put together a list of any student with a boyfriend or girlfriend.

"These students — if in lower sixth form or year 11 — can expect to find new schools in September."

However, Belfield subsequently told BBC Wales that pupils would not be threatened with expulsion, but they would be given the chance to "review their romantic situation".

Pupils with boyfriends or girlfriends will "be given the opportunity to review their current romantic situation, and my belief is that they (and their parents) will put their education first".

Ranked in The Times' 2017 A-level league tables, the boarding school charges annual fees of £34,500.

Belfield is no stranger to controversy, having previously lambasted "pathetic students pretending to be ill" and criticising female students for "wearing skirts that look like they are going to a nightclub".