The Queen can walk her corgis safely at Sandringham this Christmas.

For dog owners hoping to enjoy some fresh air and exercise with their pets at East Anglian beauty spots over the festive break are being reassured that a mysterious illness which has killed several animals has died out.

Royal aides called in vets to investigate, after a number of dogs became ill after being walked in the woods at Sandringham Park in the autumn.

Infected pets suffered vomiting, diarrhoea and lethargy, while some died within 24 hours of showing symptoms.

Animals have also been taken ill after being walked in Thetford Forest and beauty spots in Nottinghamshire and Cornwall.

Dr Richard Newton of the Animal Health Trust (AHT), who is leading the investigation into the outbreak, said: 'We haven't had any new cases of this mystery illness reported to us since mid-November so we're reasonably confident that, as we suspected, this is a seasonal problem.

'We would always advise owners to stay vigilant and contact their vet should they be concerned about their pets but we'd like to reassure owners that we think the worst of this illness has passed for this year.'

More than 370 questionnaires have been completed and returned to the team carrying out the investigation. Almost 20 per cent of these have been from owners whose dogs have shown symptoms of Seasonal Canine Illness, or SCI.

Dr Newton said: 'We now face the task of analysing the data we've received to try to find a cause for this illness.

'The likelihood is that next autumn we're likely to see a reoccurrence of cases so our aim is to arm owners with as much information as we can ahead of that.'

The questionnaires returned to the AHT show that the peak for SCI was in September. The last case reported to the charity was on 13 November.

'We know people will be getting together with their friends and families at this time of year,' said Dr Newton.

'Many will take their dogs for walks to work off some of the Christmas excess - our advice is to stay vigilant but to enjoy the Christmas holidays.'