Mr Langdown was cautioned by marine police before being allowed to proceed, but then broke the speed limit again by travelling at 48 knots, the equivalent of travelling around 52mph on land. A police launch, the RIB Mariner V, gave chase and Mr Langdown was apprehended.

As statutory harbour authority, Associated British Ports (ABP), which also owns and operates the port, is the prosecuting authority for Southampton Water and the port's Harbour Master, Captain Philip Holliday, took the decision to prosecute under byelaws that enforce a 6 knot speed limit.

After appearing in front of Southampton Magistrates on 17 September, Mr Langdown was fined a total of £2,429 (representing a fine of £700, costs of £1,714 and a contribution of £15 to the Victims Support Fund).

Captain Holliday said, 'Southampton Water is a wonderful natural resource that provides a huge amount of joy to tens of thousands of leisure sailors in the Southampton region. Although we are keen that Southampton's leisure marine community should co-exist with the ports commercial shipping traffic, our paramount concern is for the safety of all.

'In this instance, Mr Langdown was not only travelling at excess speed on a day when the water was very busy and extra care would have been preferable in any case but he had the audacity to ignore his initial warning from the police and to then actually increase his speed. I believe the penalty given to him is therefore appropriate. Any mariner who does not comply with the law is posing an unacceptable risk to all users of the port, both commercial and leisure, and I sincerely hope that this penalty will serve as a warning to others.'

Sergeant Andy Simpson of the Hampshire Police Marine Support Unit, who intercepted Mr Langdown, said, 'Speeding on the water is as unacceptable as it is on land and, in this particular case, was potentially extremely dangerous. When we stopped Langdown his jet ski was clocked at 46 knots. This is the equivalent of a motorist doing 230mph in a 30mph limit. Speed limits exist to keep people safe, and the six knot speed limit in Southampton Water is all too often ignored. Frequently, this is by boaters who are unaware that the speed limit exists, but, having been warned by us already, this jet-skier could not avail himself of this excuse.

'For the avoidance of doubt, the speed limit applies to all of the Test and Itchen, upriver from a line that runs from Hythe Pier, across Weston Shelf Buoy and continues to Weston Shore. There are exceptions to this that apply to water skiers in certain areas and other vessels with the consent of the Harbour Master. Whilst this byelaw is the responsibility of the Southampton Harbour Master, the Hampshire Constabulary Marine Unit will assist in enforcing this and any other byelaws that relate to the water. This conviction should stand as a warning to boat users that we have the capability to intercept marine craft in all circumstances. Once caught, we will work with our partner agencies to ensure a robust prosecution.'

Prior to Mr Langdowns court appearance, ABP was assisted by Mark Capon, of Marine Enforcement, which assists harbour authorities with compliance and enforcement issues.