YOU might say it's otterly ridiculous - but a family of the slippery mammals have moved into what will become one of York's most prestigious office developments.

Believed to be the first purpose-built urban otter holt in Britain, the underground lair has been dug at a secret address on the bank of the River Foss.

The holt forms a tiny - but legally vital - part of a massive new office development off Navigation Road.

The presence of the otters at the site was established two years ago with the discovery of otter spraint - or droppings - which were brought to the attention of City of York Council countryside officers.

As otters are a European protected species, a Defra licence had to be obtained to build the holt at what will become Grays Wharf, York's biggest new office development within the city walls for five years.

Legislation makes it illegal to disclose exactly where the holt is.

Agent to the scheme is Alistair Gill, a senior associate at Leeds-based King Sturge. He said: "The otter holt is screened and is not visible. All of those involved in the Grays Wharf development have vowed to keep its precise location a secret."

After the discovery of the otter family, developers sought help from international otter expert, Dr Paul Chanin, who confirmed the presence of the mammals at the site. He played a key role in the construction of the purpose-built holt.

Work is due to start on the five-floor 43,779 sq ft office scheme later this year, and expected to take just over a year to complete.

It is also an offence to carry out any work which is likely to injure, or knowingly disturb, an otter - so the holt has been carefully positioned so it will not be affected by the development.

Roger Hampson, of chartered surveyors and consultants Marriott Hardcastle LLP, said: "It was something of a surprise to find that otters were living near the proposed development."