Royal Mail has confirmed it is in discussions over a "possible sale" of part of its Mount Pleasant sorting office.
In a short statement this afternoon Royal Mail added: "The discussions are ongoing and there is no certainty as to when or whether any transaction will be agreed."
The announcement followed reports earlier today by Estates Gazette that the 501-year-old firm was in discussions with Taylor Wimpey over a £200m of the site.
If the mail giant completes the deal on Mount Pleasant, sales from properties in the capital would top nearly half a billion pounds, with more yet to come.
Earlier this month Royal Mail agreed a £101m pricetag on two of the seven plots it owns at London's lucrative Nine Elms development. This followed the group's 2014 sale of a one-acre site in Paddington for £111m.
With five more plots at Nine Elms which could be sold, the proceeds would make a sizeable dent in Royal Mail's spiralling annual pension bill.
The firm has one of the largest final salary pension schemes in the UK, which it plans to shut in March 2018 despite being in surplus.
Royal Mail said the cost of keeping the scheme open has rocketed. It estimated its annual cost would swell to an unaffordable £1.3bn.
Discussions are ongoing between unions and the FTSE group over the pension closure, with industrial action threatened if an agreement cannot be met.