Bethany Firth ruled out of World Para-swimming Championships through injury

Bethany Firth competed for Ireland at London 2012 before switching to the British team

Britain's four-time Paralympic champion Bethany Firth has withdrawn from the World Para-swimming Championships in Mexico.

The 21-year-old, who holds three world records, has an ankle injury and is not expected to return until next year.

The competition starts on 30 September.

"I thought I might have had time to recover but the competition came too soon for me," said Firth, who competes in the S14 classification for athletes with an intellectual impairment.

The Northern Ireland swimmer won three golds in Rio last summer, retaining her 100m backstroke title from London, where she competed for Ireland, and adding the 200m freestyle and the women's 200m individual medley to her tally.

Firth, who is from Seaforde in county Down, also claimed silver in the 100m breaststroke in Rio.