London, Dec 28 (IANS): Floor plans of the UK's Mi6 or the Secret Intelligence Service's central London headquarters were lost by building contractors during a refurbishment, the media reported.

The BBC said that the missing plans were not classified or intelligence documents, but the pages did hold sensitive details on the layout, including entry and exit points.

Most, but not all, of the documents were recovered inside the building after it was noticed they were missing, it added.

Balfour Beatty, the company working on the refurbishment at the headquarters in Vauxhall, is reportedly no longer working on the project.

The documents, which went missing a few weeks ago, were produced and owned by Balfour Beatty and designed to be used for the refurbishment.

The contractor kept the plans on the site at Vauxhall Cross in a secure location.

The UK Foreign Office said it did not comment on intelligence matters, while Balfour Beatty refused to because of sensitivities.

Balfour Beatty mainly carries out work in the UK, US and Hong Kong and has 26,000 employees worldwide, according to the company's website.

The BBC reported earlier this month that Balfour Beatty's order book for 2019 was expected to be more than 14 billion pounds - "significantly higher" than 2018's 12.6 billion pounds book.