by Our Sports Desk

The cost of refurbishing the Olympic Stadium ahead of West Ham’s move could rise by up to £50 million due to the complexity of extending the roof, according to reports.

The club would not have to pay any increase in construction costs however, while stadium sources say there will be no delay in completion.

The London Legacy Development Company (LLDC) — which happens to be chaired by London mayor Boris Johnson — is in talks with constructor Balford Beatty about the increased cost.

Construction Enquirer magazine has reported that Balfour Beatty has asked for an extra £50m, but the firm would not comment on the report.

The Olympic Stadium is due to host 2015 Rugby World Cup matches in September and October next year, with West Ham to move into the venue in 2016.

The work to strengthen the roof and extend it to cover the retractable seating over the running track has proved extremely complex and construction experts are using similar technology to that used on North Sea oil rigs.

The original stadium cost £429m — of the public’s money — to build and the fixed conversion fee with Balfour Beatty was agreed for a further £154m. There was however a flexible cost element to the roof work as it is unique in terms of stadium development. Should the roof end up costing an extra £50m, and stadium authorities remain hopeful it will be significantly less, that would take the final bill to £634m.

None of the extra cost will have to be borne by West Ham however. The deal it agreed last year with the LLDC will see the club contribute only £15m for a 99-year lease together with annual rent and a share of income.

It is understood any rise in cost would come out of the contingency funding and from other savings.

An E20 Stadium LLP spokesperson said: “The project still has close to two years to run and we are in no doubt Balfour Beatty can deliver the programme as planned. This is a complex project and there are always ongoing discussions about specific elements within it.”

West Ham won the right to play at the Olympic Stadium back in 2013, beating Tottenham and Leyton Orient.

Last month, Spurs brought up the possibility of a ground share with the Hammers but vice-chairwoman Karen Brady ruled out that possibility.

“In reality they probably could — but only with our permission,” she said at the time. “No one has asked us for our permission and, if they did, we would probably say no, depending on who it is — if you get my drift.”