Swiss Cottage was among stations which closed on Sunday night

The Rail, Maritime and Transport (RMT) union welcomed the negotiations with London Underground (LU).

The row centres on new rotas which, the RMT says, will leave some stations dangerously understaffed - something denied by Tube bosses.

It has already prompted two strikes, on New Year's Eve and last Monday, which each closed about 40 stations. LU said the impact was "minimal".

But the union said the situation was "chaotic" and claimed staff were working in positions for which they were not fully trained.

It has threatened to ballot its members for additional industrial action short of a strike, probably a go-slow, over claims safety was compromised during the first strike - something denied by LU.

But RMT General Secretary Bob Crow said on Thursday: "We are pleased that discussions have recommenced with LU to resolve all the outstanding issues relating to the dispute.

'Shorter' week

"No further comment will be made until the talks conclude."

It is part of a continuing row over new rotas, due to come in on 5 February, which the RMT says will displace hundreds of station staff and leave some stations understaffed.

LU said it will not compromise safety and the 35-hour working week deal, to which the new rotas are linked, was agreed by the RMT and other unions last year.