The survey said literacy and numeracy skill were a problem

The survey from the Confederation of British Industry (CBI) and KPMG found 61% of employers had concerns over staff with poor maths and English.

The survey said a shortage of skilled workers was now the biggest barrier to business in London, overtaking transport problems for the first time.

The report also revealed half of London firms were not prepared enough for a terrorist attack.

The survey of 104 businesses, employing about 500,000 people, found firms were concerned over a lack of staff with specialist skills.

Surely it is not asking too much of the government to ensure school-leavers have, at the very least, the ability to add up, read and write CBI director general Sir Digby Jones

But difficulties recruiting workers with adequate general skills - in communication and team working as well as literacy and numeracy - were also reported.

CBI director general Sir Digby Jones said: "While it is positive news that London is still seen as a good place to do business, employers are right to be concerned about the difficulty in finding staff equipped with both basic and more advanced skills.

"Business does not expect young people to have all the skills to do a specific job.

"But surely it is not asking too much of the government to ensure school-leavers have, at the very least, the ability to add up, read and write."

The survey found half of firms questioned did not have plans in place to deal with a terrorist attack or an incident such as the Buncefield oil depot blast.

Smaller companies were the least well-prepared, while larger firms were more worried about crime.