For nearly three centuries its occupants have gazed down upon what Daniel Defoe once pronounced to be 'the finest quay in England, if not in Europe'.The windows of 20 South Quay, Great Yarmouth, have provided the perfect vantage spot from which to watch the flow of River Yare from its days as a naval base for Lord Nelson, through the boom years of herring fishing to its position at the centre of the UK oil and gas industry.

For nearly three centuries its occupants have gazed down upon what Daniel Defoe once pronounced to be 'the finest quay in England, if not in Europe'.

The windows of 20 South Quay, Great Yarmouth, have provided the perfect vantage spot from which to watch the flow of River Yare from its days as a naval base for Lord Nelson, through the boom years of herring fishing to its position at the centre of the UK oil and gas industry.

Now it is another change of historic proportions - the opening of the �50m outer harbour - that has brought on to the market one of the port's most striking 18th-century quayside merchant houses.

The move of 30 Great Yarmouth Port Company staff to refurbished offices at the old Omni-Pac egg carton plant, overlooking the new harbour, has left empty what was for nearly two centuries the town's customs house, plus a neighbouring property, number 21, built much later and now adjoining it.

The three-storey properties are being marketed together freehold by Howards estate agents for �625,000, a price influenced by the recession that might be seen as a bargain for a slice of history.

Gary Wiseman, agent for Howards Commercial, said: 'The buildings have been up for sale since February, but we have only really been able to step up marketing them since

they were vacated in the last few weeks.

'We have already had a fair amount of interest from people viewing it as an investment opportunity as well as from possible owner-occupiers.'

While some parties had expressed an interest for offices, one was considering a use in the health sector, he added.

And Mr Wiseman said it might be possible to consider a high-quality apartments conversion for part of the properties.

Number 20, listed for its architectural and historical interest, was built in 1720 - four years before Defoe's pronouncement - for John Andrews, an influential herring merchant.

It was bought as a customs house in 1802 and sold to the Port of Yarmouth Commissioners, the forerunner of the port authority and port company, in 1986.

Number 21, which is also listed, was built in 1909 and used by the commissioners ahead of their purchase of the neighbouring property.

Both properties have impressive stairways, and No 20 has a striking panelled boardroom at first-floor level.

The asking price includes a park for up to 20 cars.