Image source, Reuters

The clubs and police want to avoid a repeat of violence seen at Fratton Park when the two teams clashed in 2019.

Fighting broke out outside the stadium, multiple people were injured and a police horse was punched.

Eight men were jailed for violent disorder.

On that occasion, the option of a "bubble" was not available due to the short notice of the Carabao Cup draw.

A "bubble" system was used when the two sides met at St Mary's Stadium last September and, in contrast, only two arrests were made.

Southampton FC said: "The club realises this may inconvenience some supporters, but it is necessary to ensure a safe and enjoyable match day for all."

Southampton supporters attending the match will be required to use club-managed transport.

They will travel to Fratton Park on designated coaches departing from St Mary's Stadium, with the £20 cost of travel added to the ticket price.

These will leave between 08:00 and 09:00 for a 12:00 kick-off, and fans will be required to arrive no later than one hour before their coach is due to leave.

Tickets will only be given to fans once the coaches have set off.

Everyone will be searched, and a form of photographic ID must be provided prior to boarding the coaches.

On arrival, fans will be escorted by police into the ground, while officers in protective gear, police dogs and helicopters will be deployed by Hampshire and Isle of Wight Constabulary.

Steve Humphrey
BBC South Today

It is an early start for Southampton fans as they board a fleet of coaches to take them to Portsmouth for the midday Championship match.

A breakfast burger bar is doing a healthy trade as fans wait to get on 44 coaches.

They’re getting a pat down security check as they enter the coaches.

The transport "bubble" for 2,700 Saints fans is all part of a big security operation designed to avoid any trouble between supporters of the South coast rivals.

At "bubble" matches, rival supporters are deliberately kept apart before and after the game.

Travel for away supporters is limited to official transport and the system is usually reserved for derbies and games between clubs with intense rivalries.

They frequently involve designated pick-up points and police escorts.

For both South Coast derbies this season – as was the case in 2011/12 season – away fans must travel on the bubble.

Good morning and welcome to our coverage of the build-up as Saints and Pompey are set to clash at Fratton Park this afternoon.

The last match between the two rivals was 0-0 in September so it will be hoped for more action on the pitch this time – but there is a huge police operation to ensure that’s the only place anything kicks-off.

Southampton fans are currently congregating at their home stadium of St Mary’s, where they will be bussed down the M27. There is no other way for them to get into the match.

We’ll have full coverage between now and kick off, at which point our colleagues at BBC Sport will provide you with full match coverage on their live page.