Stuart Lancaster's announcement at Twickenham on Wednesday of the Rugby World Cup training squad saw 50 players' names listed. But to quote the famous Jim Telfer 'Everest' speech he delivered to the British & Irish Lions team prior to their Test match against South Africa in 1997: "Being picked is the easy bit". Now comes the hard part of making the final 31.

As longlists go, featuring in this is the equivalent of reaching Everest's base camp. In late August, 19 players will be told to pack their bags and return to club duty having fallen short of making the final cut. Two of those named in the extended squad on Wednesday know that pain: David Strettle and Chris Robshaw both missed out four years ago.

Robshaw's journey in the last four years has seen him go from being one of those discarded to the first name in the 50-man party. Unless there is the most stunning volte-face from Stuart Lancaster, he will be the World Cup captain.

For Strettle, his recall shows a remarkable change of faith from the England coaching staff. Since he last played for England on their tour of Argentina in 2013, Strettle has continued scoring for Saracens but Lancaster has started eight different wingers at Test level; it remains a problem position.

As one of five wingers in the training squad, three are likely to make the final party alongside two fullbacks. Jack Nowell and Anthony Watson were flavour of the month for the last three rounds of the previous Six Nations so they will have to suffer the most monumentally drastic loss of form not to make the 31-man group. However, there is an opportunity for one of Strettle, Jonny May, Chris Ashton and Marland Yarde to take the last spot.

As with the brutality of naming squads, there are those who have been less fortunate, those who stood waiting by their phone in hope rather than expectation only to be told they had the summer to sit on a beach rather than in their Bagshot headquarters.

Exeter's Dave Ewers is the unluckiest. He has had an exceptional season at the Chiefs and has on occasion outplayed those picked ahead of him for England duty. In April, he nullified the sizeable threat of Tom Wood when Exeter met Northampton but Lancaster and his lieutenants deem this World Cup to have come just too soon for him.

The same cannot be said for Maro Itoje. The 20-year-old is wise beyond his tender years. A conversation with Itoje takes in rugby but also dabs of African politics and poetry. His calm, quiet voice belies his physical, robust presence on the field but his versatility is a major benefit.

His ability to cover both lock and blindside is a handy asset when pondering the limitations of a 31-man squad. This World Cup training squad may yet be looked back on as a time of acclimatisation for him and a key step in his development but there would be few raised eyebrows if Itoje makes the final cut. This season he has already started a Champions Cup quarter-final and is likely to feature in the Premiership final four on Saturday; a World Cup is the natural next stage in his rapid elevation.

Versatility also bolsters Henry Slade's claims to reach the final 31. His England exploits have been limited to Saxons appearances but he can cover fly-half, the centres and fullback. He also has that added ingredient of being a box office back and he will learn from working under Mike Catt who is an old hand at World Cups - he featured in four tournaments - and versatility along the backs.

And then there is Sam Burgess; the absence of Manu Tuilagi's sizeable quads mean England are looking for a new bulldozing behemoth in their midfield. The smart money is on the first choice pairing seeing Brad Barritt starting alongside Jonathan Joseph but a summer of working alongside Andy Farrell could see Burgess emerge as a bolter for the final 31. However, Farrell himself knows the pitfalls of premature exposure to Test rugby after his struggles in the 2007 World Cup. To date, Burgess is falling short of the qualities required from an international centre.

But if there is an area where an outside bet can gatecrash the World Cup squad it is the centres. Barritt and Joseph are the only nailed on certainties as it has traditionally been a problem position for Lancaster - 16 months ago Joel Tomkins was starting there. Both Luther Burrell and Billy Twelvetrees have had plenty of chances but they need to re-find their best form - the latter's miss-passes oscillate between sheer incisive brilliance or finding touch. Elliot Daly's inclusion is from left field from an international perspective as Lancaster has seldom called him into the camp but he has been wonderful for Wasps.

The outlier in the centres is Kyle Eastmond who had to wear the scars of being dropped three times in six months. But he is special - he offers England a sumptuous portion of devilish footwork as the All Blacks found in that first June Test in Auckland.

The date for the final 31-man squad to be announced is yet to be confirmed with the cut-off point August 31. There are still gaps to fill. While the forwards offer enough strength in depth to ignore even the claims of Steffon Armitage it is the backs where there is still indecision.

Head of Lancaster's list over the next three or so months will be working out what game plan suits this group. He will need to choose between the kick chase mode favoured by the All Blacks, the up-the-jumpers snarling performance England put together against the Wallabies in November or the harum-scarum indulgence of their win over France. Once that is sorted and the playbooks are tattooed into England's DNA, then come September 18 when Fiji arrive at Twickenham, the peak of the mountain may seem that little bit more scalable.