Its mind-boggling array of inter-locking mini-roundabouts has bamboozled many a motorist for almost four decades.

But yesterday it was a team of council workmen who were looking bemused and left scratching their heads in the middle of Swindon's infamous Magic Roundabout.

For the first time since it was created in 1972 it had been decided to add a little festive magic to the bizarre road layout by installing a Christmas tree in the centre.

After all, the Magic Roundabout is Swindon's best known landmark, is considered as a key gateway to the town and is used by about 40,000 motorists every day.

A 40ft tree was duly ordered from Lord Aspley's Cirencester Park, while 5,500 multi-coloured lights were acquired to adorn the mighty fir after cab company V Cars agreed to sponsor the venture. All looked well when a 10-strong workforce arrived at dawn yesterday to install the giant while traffic was barred from the roundabout's central zone from 7am to 11am.

However, the first hitch was the sheer size of the tree – it was 10ft taller than expected.

Undeterred, and feeling that a 50ft tree was better than a 40ft one, the team began to steadily raise it into position.

And they seemed to be on the verge of succeeding, too, until they attempted to drop Swindon's biggest Christmas tree into a prepared base.

Try as they might, and from this angle and that, the thing just wouldn't fit.

As motorists using the outer roundabout looked on with interest, various attempts were made by the increasingly frustrated work gang.

With faces as red as Santa's gown, they eventually admitted defeat and called it a day.

Now the big switch-on, which was due to have taken place tonight , has been postponed while the team goes back to the drawing board.

After making the decision to quit, Swindon council's play and landscape officer Dave Hunt, who was in charge of the operation, said: "We're obviously disappointed.

"You don't like to fail but it happened today. We had planned for a 40ft tree and were not expecting a 50ft one.

"We obviously thought about cutting the top off but it would have been a shame – it would have reduced its glory." He said the big problem was that the base the tree should have slotted into wasn't large enough.

As his thwarted team prepared to take the tree back to the depot Mr Hunt said they would now be making a larger base before trying to install the tree again.

He added: "Hopefully, we'll be able to put it up maybe one evening later this week or perhaps next Sunday – whenever the inner part of the roundabout can be closed.

"Unfortunately, there won't be any switch-on tomorrow, though."

Built as an experiment to solve a problematic junction outside Swindon Town's County Ground in 1972, the Magic Roundabout comprises five mini-roundabouts dotted around a central one.

Swindonians generally love it and consider it an ingenious piece of civil engineering, but it often annoys and in some cases terrifies visitors.

Last year it came seventh in a poll to identify the UK's 10 most dreaded transport junctions.