Lucky tossers or worthy challengers? Are England really ready to bid for No.1?

England have the chance to complete their first overseas whitewash - in a series of three matches or more - since 1963 in Colombo over the next few days.

Whatever happens in the Test, England will rise to No. 2 in the world rankings. But, if they win, it will be their first whitewash since the 2011 victory over India that took them to No. 1 and only the third ever inflicted against Sri Lanka in Sri Lanka. On top of that, England have already achieved their first series win in Asia since 2012 and their first in Sri Lanka since 2001.

All of which sounds excellent.

And it is true that, over the last few weeks, England have found a way to win in conditions which have nearly always troubled them. In developing an attack that can take wickets in Asia and a batting line-up that can score runs against the turning ball, they have developed nicely since the tour of India two years ago. Their allrounders give them remarkable depth in both departments, while the emergence of Jack Leach has helped bring the best out of a spin attack that previously lacked the control required to build pressure. On the basis that Sri Lanka's record is pretty good and that England will take confidence from this victory, it does seem fair to conclude they have made admirable progress.

But this week's talk of England reaching No. 1 in the Test rankings was just a little uncomfortable. While it is an admirable aim and it could, if results go their way, be achieved with victory in the Ashes, it could also seduce England into thinking they have made a little more progress than is really the case.

To be fair to Joe Root, he has always maintained that England are "not the finished article" and he is quite right to celebrate success. But talk of England rising to No. 1 seems premature.

For a start, England have won only two of their last 15 games away from home. They were thrashed in Australia and India - both 4-0 - beaten in New Zealand and the UAE (by Pakistan) and held to draws in Bangladesh and the Caribbean. Until several of those results can be corrected, any No. 1 ranking - while welcome - is going to feel just a little hollow.

It has to be acknowledged that Sri Lanka are not the team they once were, either. While their recent record is decent - they beat Pakistan in the UAE and had not been defeated at home by a non-Asian side since 2014 - they have been hit by a succession of retirements in recent years (Rangana Herath being the latest) and are struggling to develop replacements of a similar standard.

England might accept they have had some fortune, too. Root has - remarkably - won the toss in England's last seven Tests. While there are times that matters little, there have been other times - not least in Kandy, Galle and at Lord's against India - when that has been a substantial advantage.

That's not to detract from England's success. They won the toss a few times in India, too: it made little difference. A team still has to be good enough to take advantage. But it is a factor that has to be acknowledged.

The enduring issues remain, too. In picking Jonny Bairstow as their fourth No. 3 of the series, England have underlined their inability to fill the role since the loss of form of Gary Ballance or, before him, Jonathan Trott, while their newest pair of openers still have lots of questions to answer. Impressive as Rory Burns and Keaton Jennings have been this series, it is premature to view the former as a settled member of the side, while Jennings' long-term Test record - he averages 28.20 after 14 Tests - remains modest. It shouldn't be forgotten England were 103 for 5 in Galle and 139 for 5 in Kandy, either. That top-order batting remains fragile.

Meanwhile, England are no closer to finding a replacement pair of seamers for James Anderson and Stuart Broad. They still don't have a proven fast bowler who could give them a realistic chance of success in Australia and they were saved in Kandy - up to a point, anyway - by a couple of outrageously good pieces of fielding and final-wicket stands that added 101 runs across the game.

So England deserve great credit for their success and the progress they have made. They are developing into a highly-entertaining side with a very exciting future. But at the risk of bringing some early humbug to Christmas, let's go easy on talk of No. 1 for a while. There are substantially more difficult challenges to come.