SECURITY measures at the Forth Road Bridge are set to be tightened after a toll booth operator had water containing solvent squirted in her face from a pump-action water gun.

Mrs Lynda McArthur, 38, whose vision was temporarily blurred after a stinging sensation affected her eyes, was taken to hospital after buzzing the bridge's operations room to raise the alarm.

Last night, police officers criticised the action of a male passenger in a transit van who leant over the driver, to whom she was giving change, and squirted the liquid from the two-feet long gun.

A spokesman for Lothian and Borders police said: ``This appears to have been a childish prank that went badly wrong and it is fortunate the woman did not sustain serious eye injuries.''

A report on the incident is to go to the next meeting of the Bridge Joint Board and management has discussed it with the Transport and General Workers' Union.

Depute general manager Barry Colford said it was a matter of some urgency. ``The incident was of great concern and we are looking at ways of possibly improving security and safeguarding staff. We would not want a recurrence.''

Mrs McArthur, from South Queensferry, said: ``It happened so quickly. I was very frightened when it started stinging. At first I couldn't open my eyes.''

The van - a dark blue L-registered Ford Transit - was registered to Swift Van Rental.

The driver is in his early 30s, with collar-length blond hair, a moustache, and a chubby face. The man with the gun is also in his early 30s, of thin build, tanned complexion, and short brown hair.