A French school due to start its first teaching year this autumn has had to learn about English heritage the hard way after it was warned against unauthorised alterations to listed buildings in one of London’s best preserved Georgian squares.

Conservation officers have warned a new school about alterations to Grade 1 listed buildings at 43-45 Bedford Square and 15-19 Bedford Avenue.

Ecole Jeannine Manuel, which has schools in Paris and Lille, acquired a lease last year on a group of Grade 1 listed buildings at 43-45 Bedford Square and 15-19 Bedford Avenue to house its London teaching site.

Lady Ottoline Morrell a member of the Bloomsbury Group used to live at number 44 and the 18th century buildings were recently used as law courts.

The school applied for planning permission and listed building consent to convert the premises to accommodate 500 pupils but started on demolition and construction works before permission was obtained in what appears to have been a rush to have the school ready for the start of term in September.

Making alterations to a listed building without the permission of the local planning authority is a criminal offence. In this case consent is needed from Camden Council, which is advised by Historic England (formerly English Heritage).

Local amenity society The Bloomsbury Association alerted Camden to the unauthorised works and complained about noise from the site.

“They seem to have got themselves into a real mess by starting demolition and construction without either planning or listed building consent,” said a spokesperson for The Bloombury Association.

Fitzrovia News contacted the school and asked why works were being carried out without planning or listed building consent.

Bernard Manuel, chairman Ecole Jeannine Manuel UK, declined to answer our question directly but issued a statement saying they were extremely sensitive to the cultural heritage of Bedford Square and that they had engaged a team of professionals who had spoken at length with Camden.

“The team includes a dedicated heritage consultant with extensive experience of working with the Camden Council Conservation Officer; and an independent approved building inspector who has advised on how best to comply with Building Regulations, while at the same time respecting the fabric of the historic Bedford Square buildings,” he said.

“The project team met on site with the conservation officer in April 2015 to review the proposed works and have followed her advice in developing the design. A listed building application was submitted in May 2015, following discussions between our heritage consultant and the conservation officer. Further details were added to the application in July 2015.”

Manuel stated that works to the main building were limited to wiring, repairs to roof flashing to make the building weather tight, and reversible enhancements required to make the building comply with current building regulations.

“The internal alteration works to the modern annex at 15-19 Bedford Avenue were discussed with the conservation officer. The conservation officer confirmed that the proposed works to that part of the building do not affect the special architectural or historic interest of the listed building as a whole and — as the law makes clear — these works therefore do not require listed building consent. The façade of 15-19 Bedford Avenue is its only historic element; the remainder of the building (15-19) is of late 1980s steel frame construction,” he said.

Some works at 15-19 Bedford Avenue went beyond what was agreed with conservation officers.

Camden Council confirmed to Fitzrovia News that alterations which did not constitute significant historic or architectural significance and modest repairs would not require formal listed building consent could proceed. But during an inspection last week they found that some unauthorised works had taken place and that they were extremely concerned about this.

They informed the school that the council is considering a criminal prosecution for unauthorised works to a listed building.

However Fitzrovia News understands that as the majority of the alterations either do not require listed building consent or are not controversial the council is not at this time seeking an injunction to stop all works. Instead council officers will deploy close scrutiny to ensure no more unauthorised work is carried out.

Phil Jones, cabinet member for regeneration, transport and planning said:

“The extent of the works taking place have been reviewed in detail and some of them do not require consent as they are ‘like for like repairs’, repairs or decoration.

“However as other works requiring listed building consent have been undertaken the council has formally cautioned the owners of the property and warned them about the risk of prosecution for unauthorised alterations.

“For any changes that do require consent the council will work closely with Historic England to determine if they are acceptable on the property given its historic value,” he said.