Six Nations: The hardest calls for Lions' coach Warren Gatland as D-Day looms

Selections must soon be made for summer tour

There are always consequences when players go in search of a Grand Slam and end up being beaten so badly, they wonder how they put themselves within reach of that glittering prize in the first place. In a Lions year, these consequences are unusually severe.

Had England completed a first Six Nations clean sweep in a decade at the weekend, most of the team would have expected a plane ticket to Australia this summer. Now, the red rose contingent could easily be in low double figures and might even descend into single digits. Strong candidates should not become rank outsiders in the space of a single game, however gruesome, but the Lions' window of opportunity closes all too easily with next month's team announcement looming.

Backs: wing worries

The Welsh goalkicker Leigh Halfpenny was the outstanding Six Nations full-back, despite the free-running challenge of Stuart Hogg of Scotland and the improving form of the Lions incumbent, Rob Kearney of Ireland.

A strong candidate for the Test team, Halfpenny will expect to be joined in the squad by his fellow back-three operatives, George North and Alex Cuthbert.

With Warren Gatland, the Lions coach, expected to take 37 players, there is room for both Kearney and Hogg to travel alongside the Cardiff Blues player. The squeeze comes on the wings, where Chris Ashton of England, once the hottest of tips to take on the Wallabies, may find himself frozen out by the two Scottish wide men, Sean Maitland and Tim Visser.

As for the centre positions, Gatland has plenty of thinking to do. Again, the Welshmen have no need to fret over their summer plans: Jamie Roberts and Jonathan Davies are certainties. It is also hard to imagine Brian O'Driscoll being left behind, assuming he is not banned until next season for his spectacularly pointless stamp on the Italian flanker Simone Favaro at the weekend. O'Driscoll is thought to have identified this coming tour as his final rage against the dying of the competitive light.

If Gatland decides the limited but undeniably powerful Manu Tuilagi is also worth a place, he will be in need of another specialist inside centre. They are thin on the ground, so Brad Barritt could make the cut.

Tight forwards: Welsh power holds all the aces

Gethin Jenkins and Adam Jones, the two senior Welsh props, are already on the plane, figuratively speaking. Being a front-rower of yore and the boss of Wales into the bargain, coach Gatland cannot conceivably look past the two of them as leading candidates for the Brisbane Test. He is also certain to include Dan Cole of England, even though he is in a scrummaging trough.

When the hard-working Dubliner Cian Healy stamped on Cole's ankle during the Ireland-England game, some felt he had done his Lions chances irreparable damage. Now he has served his time, there is no reason to think he will not travel. Assuming Gatland does not go fishing in foreign waters for the likes of the exiled Andrew Sheridan, the last vacancy should go to a prop capable of operating on both sides of the scrum. Another Welshman, the reliable Paul James has a shout.

Richard Hibbard of Ospreys is leading the hooking charge – of the two England challengers, Dylan Hartley has a better argument for selection than Tom Youngs – and this being a Welsh age, the current red dragon locks Ian Evans and Alun Wyn Jones are clearly in pole position, especially as the main Scottish candidate, Richie Gray, is struggling for form and fitness. With yet another Welshman, the injury-prone Luke Charteris, still present in Gatland's affections and Donnacha Ryan of Ireland impressing many with his hard-bitten work in the Six Nations, no English lock can rest easy.

Loose forwards: the most difficult choice comes at No 8

Gatland is said to have been deeply disappointed at Sam Warburton's reluctance to perform the captaincy duties for Wales against England on Saturday, but that is unlikely to stop him considering his favourite open-side flanker for the leadership role in Australia. With Justin Tipuric also mounting an open-and-shut case for inclusion, and with the England captain Chris Robshaw every bit as certain to travel (not least because he is equally capable in the blind-side position), the main breakaway contenders are obvious. This is good news, for even without the ball-winning maestro David Pocock, the Wallabies will be very strong in this department.

There are plenty of short-side options for the Lions, too. Another multi-tasking back-rower, Sean O'Brien of Ireland, will surely be selected – there will be a steward's inquiry if not – and it may be that two England men, Tom Croft and Tom Wood, join him in the business class lounge at Heathrow.

Toby Faletau of Wales is the early favourite for the No 8 berth, leaving players as good, in their different ways, as Jamie Heaslip of Ireland and the two Scots, captain Kelly Brown and broken-field specialist Johnnie Beattie, scrapping for a place. No 8 will be among the most difficult positions to fill: although Faletau's form against England was up a notch on previous outings, he does not believe he is playing anywhere near as well as at the last World Cup. Gatland needs a moment of inspiration here.

Half backs: Sexton's absence helps his case

Sometimes, the best way of underlining your potential value to a Lions party is to be off-limits to your national team when they are going through a rough spell. Jonathan Sexton of Ireland is aware of this fact of rugby life, although he wouldn't dream of mentioning it in public.

Had Sexton not given his hamstring an almighty twang during the tough game with England in Dublin last month, the most gifted attacking stand-off in European rugby might have been dragged into the morass of his country's defeat in Rome. As things turned out, he merely looked down on it from the stand. Sexton will fly as warm favourite for the Test berth in Brisbane on 22 June, backed, it is generally assumed, by Owen Farrell of England, whose implacable competitive nature means the No 10 shirt for the subsequent Tests will be hotly contested. As for Jonny – what's his name again? – Wilkinson … well, we know he wants to go, and that makes him an intriguing outside bet.

In the scrum-half department, the most interesting contender is Greig Laidlaw of Scotland, not least because he can also do a turn at No 10 and kicks goals in his sleep. The bull-like Mike Phillips is the main man for the tour, even though it is possible to make a case for Lloyd Williams being the best "pure" scrum-half in Wales. Ben Youngs of England is a contender for the final slot.

Championship by numbers: best and worst

74: Leigh Halfpenny's 74 points saw him finish as the top points scorer in the tournament

5: England scored five tries, including Manu Tuilagi, their worst return in Six Nations history

88 per cent: Greig Laidlaw's success rate for kicks at goal, missing just three of his 25 attempts

534: This year's total points tally of 534 is the lowest since the Six Nations began in 2000

4: Alex Cuthbert finished top tryscorer, going over four times

35: Wales won 35 of their 40 scrums in the tournament

2006: Scotland's third-place finish is their highest since 2006