Shelved plans to install new jet fans in a closed-off tunnel on the A299 Thanet Way could have taken more than 18 months to complete, it has been revealed.

A contraflow system was introduced on the coastbound stretch in June so faulty ventilation equipment in the Chestfield Tunnel near Whitstable could be replaced.

Kent County Council (KCC) originally said it would take three months to manufacture and install the bespoke fans, which are used to clear smoke in the event of a fire and toxic fumes spewing from vehicles.

But transport bosses have instead decided to only patch up the equipment, conceding the initial proposal would have required a full redesign and seen the contraflow remaining in place for a year and a half or longer.

However, the temporary road restrictions - which snarl up traffic as drivers can only use one side of the tunnel - will return when the fans are eventually fully replaced.

KCC has confirmed it is committed to carrying out the work, and potentially within the next two years.

The authority’s cabinet member for transport, Neil Baker, spoke to KentOnline inside the Chestfield Tunnel, explaining why the new fans cannot be installed now.

“There are not many places you can get fans. You can’t walk into a DIY store – these are incredibly large bits of equipment,” he said.

“A decision was made to actually, having looked at it and got the consultants in and seen what could be done, if we were to get a brand new set of kit in, up to modern regulations, that would involve having the contraflow in for a significantly longer period, perhaps 18 months, perhaps longer.

“Absolutely it's been a delay and we don't like delaying the public [but] the reality is this isn't a set of equipment you can get off the shelf

“Even [with] the repair work we're doing, we have to source those spare parts from all over the place just to get the system working for a little bit longer before a new system gets designed and put in place.

“End of October is what we're looking at. We're not getting an exact date yet because obviously once all of the equipment has been brought back, it needs to be tested in real-world environments.”

Cllr Baker could not give an estimated cost on the new fans or a “hard and firm timescale” on when they could be installed given how specialist the equipment is.

He says of most importance is that it is reliable to avoid ongoing closures along the stretch between Whitstable and Herne Bay.

The Conservative added efforts will be made to retain a 40mph speed limit through the tunnel indefinitely in the interest of safety.

Since being introduced in the 1990s, the jet fans have been activated manually five times – all of which were for emergency smoke management.

The vents are also used throughout the week and trigger when there are high pollution levels from older vehicles or stationary vehicles due to incidents or slow-moving traffic, and when the tunnel becomes misty or foggy.

They have a lifespan of about 25 years, meaning the existing set-up is already outdated, and bosses hope replacing the fans with higher-tech units will keep the tunnel in sync with safety guidelines.

The Mont Blanc tunnel fire in March 1999 claimed the lives of 39 people and has been credited as one of the key reasons there are such stringent regulations.

Prior to the current contraflow being introduced, similar restrictions were imposed earlier this year to allow for the reconstruction of a coastbound stretch near Whitstable.

It will mean a contraflow having been in place for six months of this year should it eventually be removed by October 31.