Buzz was owned by Dutch airline KLM

The Irish airline does not legally need the Office of Fair Trading's approval to go ahead with the takeover.

But if the Competition Commission concludes the deal was uncompetitive, Ryanair then could be forced to sell all or parts of Buzz.

The takeover deal should have been given the green light by the OFT at the beginning of April.

But a decision was put off because of competition concerns.

A spokesman for the OFT told BBC News Online it was up to Ryanair to go ahead with the merger, although the regulator was still looking at the case.

"If need be, action can be taken after the merger has taken place," he said.

Reduced price

A statement from Ryanair said: "This is entirely due to the very tight schedule that Ryanair and KLM have adhered to in order to complete this rescue of Buzz and save 130 jobs."

"We will continue over the coming two weeks to liaise closely with both the CAA and the OFT and look forward to obtaining their approval in due course of the purchase and rescue of the core operation of Buzz ... from 1 May onwards."

Ryanair is taking over 10 aircraft and 130 staff working at Stansted airport.

The takeover will allow Ryanair to expand its reach from Stansted as both airlines have major hubs there.

Ryanair acquired Buzz from Royal Dutch Airlines KLM for 20.1m euros.

The Ireland-based low-budget airline said the acquisition was reduced from its original sum of 23.9m euros "as a result of a number of issues which arose during the due diligence process."

Meanwhile, Ryanair said bookings for the 12 old Buzz routes were going well.