Holders England have won their first two Six Nations matches as they aim to become the first team to win the tournament outright three years in a row.
Scotland have not beaten the ‘auld enemy’ for a decade and Barclay knows they will have their work cut out in Edinburgh this weekend.
“They’ve obviously won their first two games [against Italy and Wales], two quite different games, won in different fashions,” said the back-row forward.
“They are one of the best teams in the world, their record is fantastic. They come here as massive favourites.
“They are a quality side with the quality players throughout. It’s a big challenge for us to stop them.”
He added: “I went into the club on the week off and just had a little chat with some of them [Scarlets’ Wales contingent] but the footage is there for you to see their strategies.
“They [Wales] gave away two penalties in the whole game – I don’t know if that’s ever been done before, that disciplined.
“They had a very clear strategy, a few calls here or there and the game could have gone the other way.”
Sign up to our mailing list here and we’ll keep you up to the minute with weekly updates from the world of rugby.