Moeen Ali is about to make his Test debut as a batsman whose improving off-spin helps to balance England against Sri Lanka at Lord's.

But if it transpires bowling eventually overtakes batting as his primary skill, and lands him a significant international career, he will not be complaining.

Moeen, 27 next week, will bat at number six and is expected to get through his share of overs if England's frontline pace attack do not run through Sri Lanka in the first Investec Test.

But he already has a doosra at his disposal - albeit one in prototype stage, following expert tutorials from Worcestershire team-mate Saeed Ajmal - and it is not too great a leap to suggest he might one day be a frontline spinner in the post-Graeme Swann era.

Asked if that scenario appeals to him, Moeen said: "Definitely, 100 per cent yes.

"I would love to. I think I will definitely improve and have potential to be a good, top spinner."

Could he be Swann's replacement then?

In the long term, perhaps, but Moeen knows that is not his job this week - in a team set to feature him as one of three debutants alongside pace-bowling all-rounder Chris Jordan and opener Sam Robson.

"I think in time, definitely," he said, of his succession to Swann.

"I am not here to try and replace him; I am here to do exactly what I've been doing at Worcester, and doing a good job with the bat and ball and try to contribute and win the game for England."

Moeen has begun to learn the finger spinner's modern variation, the doosra, in mid-career - but is in no doubt any emerging specialist should be perfecting the art as soon as possible.

"Being an off-spinner coming through now, if I was just bowling normal off-spin, guys can get hold of you easier than probably a left-arm spinner," he said.

"If you get something different or mystery or even just a little bit of doubt in the batsman's head, it makes a massive difference.

"If you get one early, the guys hesitate to use their feet, knowing that you've got it.

"Saeed says half the time he doesn't have to bowl it, because people just know he's got it."

Depending on the flick of a coin on Thursday, Robson will have the chance to impress long before Moeen does.

There is much confidence behind Middlesex's Australia-born batsman, including from Moeen - who was impressed last winter on the Performance Programme down under and in domestic opposition.

"Sam is one of the best openers I have seen on the county circuit," said Moeen.

"He knows his game inside out - very determined and a proper, rock solid batter.

"He leaves well, plays straight - he has all the shots.

"He is a top batter, and a great guy."

Robson's Australian provenance is no issue to Moeen either.

"I don't see him at all like an Aussie - I just see him as a normal person," he added.