“I just went out hard but wasn't expecting that. "

Paralympic Champion Josef Craig broke his own S7 world record to win the mixed classification 400m freestyle gold on day two of the British Gas Swimming Championships in Sheffield.

The 16-year-old from Tyneside beat his previous lifetime best to touch in at 4:41.13.

“I'm not fully rested for this event so to post that time is fantastic,” said Craig. “I just went out hard but wasn't expecting that.

“I've been around about my best time for a while and I wanted to push it on.

“Tonight felt the right time to do that and I'm glad because Jonathon Fox had an outstanding swim to dip under the old world record also.”

Fox was also under Craig’s old world record as he set a five second lifetime best to take the silver in 4:42.54 while S8 Paralympic silver medallist Ollie Hynd was third in 4:31.13.

In addition, Fox broke his own world record in the men's 100m backstroke event, clocking in a 1:09.52.

Paralympic champion Jessica-Jane Applegate was also in record-breaking form, shaving 0.7 seconds off her own 200m freestyle S14 British record to win gold in 2:11.47.

Fellow S14 swimmer Natalie Massey took silver in 2:19.01 and Perth’s Reagan Doig (S14) was third in 2:24.03.

In the women’s mixed classification 400m Freestyle final Hannah Russell won the gold in 4:40.89.

The S12 Paralympic silver medallist looked comfortable and was pleased with her performance.

“I was really nervous this morning so I wanted to go faster tonight,” she said. “I wanted to work on my stroke length in that race and I'm pleased because it was a lot better in the final.

“It gives me massive confidence to do this in heavy training so that time is great.”

The silver medal went to S10 British record holder Tully Kearney in 4:48.77 with bronze going to Ellie Simmonds (S6), who touched in 5:44.89.

Romford Town’s Amy Marren (S9) took the title in the mixed classification 100m Butterfly final in a lifetime best of 1:11.10.

She out-touched Claire Cashmore (S9) who won silver in 1:12.80 and Gemma Almond (S10) who was third in 1:10.72.

James Clegg (S12) topped the podium in the men’s mixed classification 100m butterfly final, touching in 1:00.13 ahead of James Hollis (S10), who won silver in 1:00.32.

Millfield’s Morgyn Peters (S9) was third in 1:05.49.

Finally, Ben Proctor won the gold in the Men’s mixed classification 200m freestyle final.

Proctor (S14) set a new lifetime best to win in 2:01.55 ahead of Jack Thomas (S14) who also set a personal best of 2:04.17 to take silver and S14 swimmer Craig Rodgie took the bronze in 2:04.43.

The 2013 IPC Swimming World Championships will take place in Montreal, Canada from 12-18 August. Featuring 650 athletes from 60 countries, it will be the biggest gathering of international swimmers since London 2012.