England manager Martin Johnson has warned his side that they must lift their levels of performance if they are to clinch a first Grand Slam since 2003 against Ireland next weekend.

Tom Croft scored England's only try as they struggled to a 22-16 victory against Scotland at Twickenham on Saturday and Johnson, captain in 2003, has demanded improvement.

"Our mistakes kept them in the game. There were too many turnovers. The second half started brighter but we couldn't land the killer blow," he said.

"We had three or four cracking chances to score and couldn't get in. They hassled and harried and fought and got away with a few things at the breakdown. It was a mess at the breakdown which suited them. They knocked us out of our stride a bit.

"But we battled through and we won. It was a good fight. All the guys are pretty flat which is not a bad place when you have won four."

Johnson could be without captain Mike Tindall in Dublin after the centre left the fray at half-time with an injury to his left foot. He collected the Calcutta Cup from Princess Anne, his future mother-in-law, at the end but left Twickenham in a protective boot and was due to undergo precautionary X-rays.

"There are a few battered bodies about. It was a pretty tough game," he said. "But it was not a bad game for us to go into next week. When everyone is telling you how good you are it can leak in a little bit. We've got lots to be better at. We'll be in a fight next week. We know we can play a lot better than that.

"We've got to make sure we are a bit smarter the next time we play. Scotland came here to fight for their lives and they did. I'd be happier in a way going to Dublin next week off the back of that game rather than scoring a lot of points and having it easy today. It focuses everybody's mind."

Scotland flanker John Barclay was sin-binned in the second half after slapping the ball out of the hands of replacement scrum-half Danny Care, who had come on for Ben Youngs. Croft's try came just moments before Barclay's 10-minute spell in the sin-bin was complete but Johnson had no sympathy with the Scots.

"I didn't really see Barclay's incident," Johnson said. "If you ask me they probably got away with quite a bit through the game. If you ask me they had it coming. Far be it for an Englishman to have a grievance."

Jonny Wilkinson replaced fly-half Toby Flood in the second-half and added a penalty and a conversion to Flood's four penalties. For Scotland Max Evans supplied the touchdown with Chris Paterson adding two penalties and a conversion while 21-year-old fly-half Ruaridh Jackson notched a first-half drop goal.

"We've got Wilko on the bench and that's not a bad place to be. Banners [Matt Banahan] was outstanding," Johnson said. "He gave us impact but we couldn't quite land the killer blow. We had them on the ropes. They looked tired but we didn't quite push them over the edge.

"They defended well and there were some good cover tackles. You have to keep on battling. We've won four from four in the Championship. It will be good to go away for a real tough game in Dublin. We've had three on the trot at home, two of which we have been heavy favourites for. It's good to go away and play Ireland, a very smart team. They will be smarting after yesterday. It's a cracking game for us to play. We've earned it."

Scotland head coach Andy Robinson was bitterly disappointed after seeing his side slump to their fourth successive defeat. "It was a very good Test match. We had to control the set piece and we didn't. It was disappointing to lose John [Barclay] at that point," he said. "We are really disappointed. There was a huge effort put in by the players. They have put their bodies on the line and it was tremendous the way they went about the game. The guys have worked hard and it is important we keep on improving."