England defence coach Felix Jones says he will have no qualms trying to stop his native Ireland's bid for a second straight Six Nations Grand Slam at Twickenham on Saturday.

Jones joined England boss Steve Borthwick's staff after helping South Africa win last year's World Cup in France.

"It's not a deal, it's been done before, I've coached against Ireland twice before," the 36-year-old Dubliner said at Twickenham on Friday.

Jones's situation is not unusual in modern professional rugby -- former England international Andy Farrell is the head coach of Ireland.

"I think when you go into coaching you have to accept that there's only so much time you'll be with certain teams before you move on," he said.

"There's plenty of ex-English coaching staff members on the Irish team as well. It's just the way it is."

Ireland will retain the Six Nations title with a game to spare if they record their fourth successive bonus-point win of the tournament against England.

Borthwick, a former England captain, has labelled Ireland as the best side in the world, even though they once again failed to get beyond the quarter-finals of the World Cup last year, thanks partly to a lopsided draw.

Jones said there was little to choose between world champions South Africa, Ireland and New Zealand -- the top-ranked sides.

"So it's one, two, three South Africa, Ireland, New Zealand and it's very tight between them," he added.

Jones is known for favouring an aggressive "blitz" defence, with the aim of stifling attacks at source.

But sheer speed can counter any system, as England found to their cost during a 30-21 Calcutta Cup defeat last month, when Scotland wing Duhan van der Merwe ran in a hat-trick of tries.

"We're hoping to put in an 80-minute performance, something that we feel we probably haven't put together yet in the first three games," said Jones.

"We've got to be on it for 80 minutes because a single lapse -- Ireland have shown repeatedly the capability to cut you open."

England are third in the Six Nations table after three games, beating Italy and Wales before their defeat in Edinburgh.