Thousands of police officers preparing for a protest march over pay have been warned to visit the lavatory before taking to the streets, to bring their own sandwiches and not, under any circumstances, to cause trouble.

A definitive guide to protesting has been issued by the Police Federation to up to 15,000 officers from all 43 forces in England and Wales who will demonstrate today over the Government’s reneging on a pay deal.

Officials, anxious to avoid embarrassing scenes, have urged the protesters to ensure that they retain the moral high ground and do not make it difficult for colleagues policing the march.

The guidance for the occasion — it is the first time that police have marched to demonstrate their anger over a pay deal or unhappiness with a Government reform programme — warns that other groups might stage counter-demonstrations.

It states: “We would ask that you do not react to any taunts; do not get involved and allow our Metropolitan Police colleagues to police as they see appropriate.

“Remember. We have the moral high ground. We will continue to conduct ourselves with dignity and pride.”

The guidance for the Central London march, which will pass the Home Office, also suggests that officers should wear suitable and comfortable clothes and footwear in the event of inclement weather. It adds: “Unfortunately we are unable to provide you all with refreshments but there are plenty of shops, cafes and restaurants in the area or you may wish to bring your own.”

The guidance advises officers to use the lavatory before setting off as there are likely to be queues at those on the route. Officers will lobby MPs over the decision of Jacqui Smith, the Home Secretary, not to backdate to September a 2.5 per cent rise for police in England, Wales and Northern Ireland. They say that this means that their rise, paid from December 2007, amounts to 1.9 per cent and therefore breaches the deal.

Ms Smith will hold talks with Police Federation leaders after the rally to discuss the dispute and a multi-year deal for the future. The timing and place of the meeting is not being disclosed for security reasons, the Home Office said.

While it is the first time that police have marched, they have previously held rallies in London to protest against Conservative and Labour Government proposals on conditions.

Police are banned from striking by a 1919 Act of Parliament after strikes in London and Liverpool when officers refused to go on duty.

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