Two children in Fife have been infected by the disease and investigations are under way to establish whether the cases are linked.

Fife NHS board said the children - one a primary school pupil and the other of pre-school age - became ill last month.

The primary school child has been immunised with one dose of the MMR vaccine, the other has not been given the inoculation.

Figures released yesterday show that fewer children in Scotland were being inoculated using the MMR jab, sparking warnings of a possible outbreak of measles, mumps or rubella.

The proportion of children being given the three-in-one vaccine dropped to 89% last year compared with 93% the year before, according to NHS statistics.

The decline comes amid concern that the vaccine could be to blame for a rise in childhood autism, a connection rejected by experts.

Both figures were well below the 95% "herd immunity" rate considered by experts to be the level that gives enough protection to the population as a whole.

But the figures also suggest that the decline in take-up of the vaccine may be bottoming out. By the end of December, the quarterly take-up rate had fallen to 86.6%.

That figure represented a decline of just 0.3% on the previous quarter - the smallest quarter-on-quarter decline of the year.

Dr Mac Armstrong, Scotland's chief medical officer, has praised those parents who opted for the MMR vaccine.

He defended the three-in-one vaccine and said the allegations made against it have not been proved.

Dr Armstrong warned that the threat of an outbreak of measles, mumps or rubella would remain as long as children were not vaccinated.

An expert group has been set up by the Scottish executive to study the MMR issue.