Gregor Townsend expects the British and Irish Lions players left out of Scotland's side to face England in their Six Nations opener to "rise to the challenge" after their omissions.

Fellow Lion Chris Harris is among the replacements after head coach Townsend opted for Huw Jones at outside centre.

"Form is a key factor in selection," Townsend told BBC Scotland.

"They are big decisions because Ali has played so much rugby for us over the last five or six years and Chris has played really well for us too.

"We believe we're not only selecting the players in the best form, but it will also get the best out of the guys that have missed out.

"They've got to rise to the challenge of getting back to their best form and both Ali and Chris are not far away from that."

Another Lions duo, Zander Fagerson and Hamish Watson, also missed out on the matchday 23 - although Townsend explained the Calcutta Cup game at Twickenham came too soon for them as they make their way back from injury.

Fagerson has only just returned to full training after two months out while Watson played his first match for Edinburgh against the Sharks last weekend after an extended spell on the sidelines following a concussion against New Zealand in November.

"Hamish missed two-and-a-half months of rugby. He only got back to playing last weekend and while he went well it's a big jump for him to go from that one game into Test rugby, especially when the competition for his position is so high," added Townsend.

"Luke Crosbie's got the opportunity this week because he's been playing so well for Edinburgh and playing well in big games. The two Saracens games stand out in particular."

Scotland are unbeaten in their last two visits to Twickenham, fighting back in an epic 38-38 draw in 2019 before finally ending their 38-year winless run at the home of English rugby in 2021.

That triumph was played in front of an empty stadium during the Covid pandemic and Townsend - who has been preparing his team with warm-weather training in Spain this week - knows this Saturday will be a different proposition.

"The challenge of playing England at Twickenham with 80,000 people there, with the record they have against us over a long time, it's going to be a really tough game for us," he said.

"We'll have to be at the level of accuracy, effort and togetherness that we were two years ago and probably more so, because they'll have the crowd and the noise behind them to help them at times.

"It's only a factor if you let it become one though - we've shown that in big environments.

"A lot of players were involved in 2019 when we didn't get things right in the first half but when we got things right in the second half that was what was most important, not whether the crowd was noisy or not."