Brighton council said the MMO2 Airwaves Tetra mast was installed on top of Theobald House, in Brighton, before it, as the landlord, had consented.

A spokesman for MMO2 said they had erected the mast in "good faith" after consulting the council last year.

The masts are used by 29 police forces in the UK to provide radio coverage but opponents claim they can damage health.

It is surprising a company of this stature has walked in and installed this equipment without the right consent particularly given public anxiety about these masts Simon Burgess, Brighton council

A council spokesman said the mast in Brighton was put up six to eight weeks ago without consent and was brought to their attention by residents.

The council believes the phone company accessed the high-rise building and tapped into its electricity supply without permission.

Simon Burgess, the councillor in charge of the property said: "Legal advice is being taken and we are taking steps to get the equipment removed.

"It is surprising a company of this stature has walked in and installed this equipment without the right consent particularly given public anxiety about these masts."

An MMO2 spokesman said the council had been told about their intentions.

He said: "We were in consultation with Brighton and Hove Council a year ago and went ahead building it in good faith but subsequently we learnt the council had issues with that.

"We are working with them closely to address these issues, the important factor being to provide radio coverage for the Sussex constabulary in the centre of Brighton as part of the new airwaves network."