Police are warning fans to be on their best behaviour at Swindon's crunch derby game with Bristol Rovers on Saturday or face a night in the cells.

Extra officers from Swindon and Avon and Somerset Police have been drafted in for the match which will see Town promoted to League One if they get a point. The game is also vital for Bristol Rovers who are battling to make the play-offs.

There were violent clashes when the two teams met at the County Ground in December. Shoppers looked on as police got to grips with 40 fans in a brawl outside the Bedroom bar in Bridge Street.

Supt Peter Kelk, of Avon and Somerset police, said the day would be policed robustly.

"Avon and Somerset Police have worked closely with Swindon police and both clubs in the build-up to the game," he said.

"The fixture on Saturday is important for both clubs so we expect tensions to be high but urge supporters to enjoy the game and do their part in ensuring the game is trouble-free.

"There will be a substantial police operation in place throughout Bristol."

Police say anyone involved in any kind of trouble risks a football banning order, barring them from every ground in England and Wales.

A Swindon Town spokesman said: "Nearly 2,000 fans will be making the trip and we are sure they will all be committed to on-field matters."