Warren Gatland says Wales' first-half performance in the Six Nations defeat by Scotland was one of the worst halves of his 30-year coaching career.

Gatland praised his squad's character for the second-half performance.

"I think I have got to apologise for the first half," Gatland told S4C.

"It's probably one of the worst 40-minute performances in my whole rugby career as a coach.

"We were terrible, shocking. The discipline was poor, and we didn't nail some things."

Gatland made changes at half-time, with replacements Elliot Dee, Tomos Williams and Ioan Lloyd impressing, while back-row duo Aaron Wainwright and Tommy Reffell were outstanding.

Wales responded with four tries, falling just short of completing the biggest comeback in Six Nations history.

"The message at half-time was to do what we wanted to do in the first, bring some tempo, play with a bit of intensity and play some rugby, nothing flashy," said Gatland.

"I think some guys came off the bench and had some impact, we were so slow in the first half, things like opportunities for quick taps to get us back in the game.

"The players should be disappointed with the first half but proud for the second half, they didn't throw the towel in and could have won the game.

"To do what we did, be 27-0 down, other teams might have shown less character and start thinking about next week, even throw in the towel.

"We didn't do that. They kept fighting and put themselves in a position to win. That showed real character"

It was Scotland's discipline which disintegrated in the second half with two yellow cards but Gatland was not happy with a penalty given away by Wales wing Josh Adams before the interval.

Adams threw the ball into the crowd to stop Scotland taking a quick line-out, with Russell punishing the hosts with a penalty.

"When you don't nail some line-outs and give away stupid penalties, the Josh Adams one was dumb," said Gatland.

"What's the difference between the game? It's Josh Adams throwing the ball over the touchline and being penalised for three points. There's some positive learnings from that.

"When you think about it, that's the difference between winning and losing the game."

Wales finished with a very young side after the replacements were introduced and Gatland says the talented rookies will learn with experience.

"That's the thing with putting youngsters out, you can't coach experience," said Gatland.

"When you're out there in front of 75,000 people making that much noise, and the pace is quicker than club rugby, sometimes that takes time for players to get used to.

"We'll need a little bit of leeway, but it's still Test rugby and it's about winning. That's what we've got to focus on.

"We need to be critical, tough on ourselves and look at where we can get better as a team."

Wales travel to face England at Twickenham next Saturday with Steve Borthwick's side edging a hard-fought away win against Italy.

"We've just got to play like we did in the second half," said Gatland.

"We've got to learn from that experience. England have had a tough win today.

"They're in a rebuilding phase. We'll go there with a lot of confidence we can build on that second-half performance and belief. That's the biggest thing."

Wales fly-half Sam Costelow will be a doubt for the Twickenham match after failing a head injury assessment (HIA).