The contractors had the dry run at ground level for the job which is now taking place between the 72nd and 94th floors of the country’s tallest tower.

The 500 tonne spire is made from 800 pieces of steel.

Severfield Rowen Chief executive Tom Haughey said: “You only get one chance when you take big pieces of steel up to that height and we wanted to make sure it fits perfectly so we have been doing trial assemblies at the yard next to Dalton.

“They are the actual pieces we will use. What we do is break them back down into manageable components, then take them down to London and reassemble them into pieces that can be lifted by a crane.

“There are always challenges and the biggest challenge isn’t in making the steel it is always in the installation at that height.

“We are doing the installation in London now and it should be finished in the next few weeks, subject to the weather not being windy or foggy. It is a great moment for the company.”

Mace said: “Located off-site on an airfield in Yorkshire – where the spire was pre-fabricated and pre-assembled – the team, led by the steel design and erection team Severfield Rowen, undertook a full pre-assembly trial programme of the spire components, which was also attended by the Health & Safety Executive.

“The focused familiarisation with the process – trial lifting operations of pre-assembled components and optimisation of the number of components to be lifted – was invaluable for the specialist erection team ultimately creating a safer more efficient environment on site.”