Formula One chiefs yesterday revealed investigations into Michael Schumacher's crash at Sunday's British Grand Prix showed the much-criticised gravel trap had ''performed satisfactorily.''

Race winner David Coulthard and runner-up Eddie Irvine were unhappy with the safety arrangements at Silverstone, but preliminary indications are the gravel trap had done its job.

A FIA statement explained: ''The gravel trap performed satisfactorily in a worst-case

situation. Despite much comment there are no simple answers to the problem of slowing an out-of-control car. The measures are under constant review.''

Irvine had suggested the gravel trap could be built to slope uphill, thereby decreasing the car's speed as it careered off the track. The black box from Schumacher's car has been downloaded and it shows he was going at 191mph when he first braked, his wheels locked at 127mph and he hit the tyre wall at around 67mph.

The German left Northampton General Hospital with his wife Corinna yesterday.

Joan Rumsey, nursing director at the hospital said: ''Michael had a quiet night. Last evening he was playing cards and watching television with his wife. This morning he has been reviewed by the surgical team who are very pleased with his progress.

''Michael wants us to express his thanks and to say how overwhelmed he was to receive all the best wishes from his fans, which have come from all over the world.''

Surgeon Bill Ribbans, who carried out the operation on Schumacher's broken right leg, said the driver was recovering well and was ''very determined'' to get better.

Ribbans said Schumacher had suffered

tissue damage in his leg, causing swelling around his joints, as a result of the impact of the crash.

Surgeons inserted a foot-long pin into his right leg after discovering breakages of his right tibia and fibula.

Finland's Mika Salo will replace Schumacher at Ferrari, the Italian team announced later.

qFerrari isued a statement yesterday about the accident which said:

Following the accident of Michael Schumacher at the British GP, Ferrari are conducting a full and urgent investigation.

What has been established so far is that the accident was caused by a sudden loss of

pressure of the rear brake circuit.

This was due to the loosening of a brake bleed nipple on the left rear caliper.

The reason for this loosening of the nipple has not yet been established.

This component had been checked as part of the Saturday evening race preparation and there had been no subsequent servicing of that part.

The data shows no problem either in the warm-up, or indeed, in the braking man-oeuvres for the first half lap of the race.

Ferrari will continue to try to establish the reasons for this failure.