Mum of UK's biggest family reveals she was 13 during first pregnancy and her partner was 18

Sue Radford made the sensational revelation on her reality show 21 Kids and Counting. Picture: This Morning

Viewers of 21 Kids and Counting were left in shock at the revelations after realising their sexual relationship would have been considered illegal.

The mum to Britain's biggest family has shocked viewers after revealing she first fell pregnant at 13-years-old, and her partner was an 18-year-old man.

Sue Radford made the sensational revelation on her reality show 21 Kids and Counting, which follows her as she gave brith to her 21st child, Bonnie Raye after just 12 minutes in labour.

Viewers were shocked to learn that Sue was just a schoolgirl whens he conceived her eldest daughter Rosie, while her now husband Noel was a legal adult and fiver years older than her.

A stunned viewer tweeted: "They are lovely kids but I can’t help but feel a bit weird about the fact when he was 18 he got a 13 year old pregnant #21kidsandcounting."

Another added: "Everyone commenting on what a lovely family they are, how old does a guy have to be before getting a 13 year old girl pregnant is creepy at best, irrespective of whether they get married and stay together?

"A particularly disgusted fan wrote: "I can't get over the fact that an 18 year old got a 13 year old girl pregnant I mean that's a crime!"

21 kids and counting. Picture: This Moro

The Radfords also revealed how they spend their Christmas holidays, with the couple claiming to spend between £100 and £250 on presents for each of the 21 children - working out at a total of £5,250.

Sue and Noel first shot to fame in 2012 when they appeared on the Channel 4 documentary 15 Kids and Counting.

The couple, who finance themselves with the profits from their bakery and claim only child benefit, say they don't want anymore saying they are looking forward to grandkids.