A Knightsbridge house could be tripled in size by drilling that goes 50 feet underground.
But the neighbours of the homeowner who wants to do this has aren't too happy, as Marcus Powell reports.
More top news
Stamp duty is to be abolished for first-time buyers on properties up to £300,000, Chancellor Philip Hammond has announced in his Budget.
The money will help pay for mental health and counselling services, regeneration in the west London neighbourhood and a new community space.
The small device was hidden in a grate in the ceiling in the only customer toilet at a Starbucks coffee shop.