The discovery was made during a dig at Wisbech Library in the Crescent in the process of a massive £2.5 million refurbishment of the premises.

The library received £2 million Lottery funding, with Cambs County Council footing the remainder of the bill, to extend and remodel the ground and first floor.

The excavation had to take place as part of the planning process for the library changes and, due to the library's position in the centre of Wisbech, there was a high probability of buried archaeological remains.

Some burnt wood was found and, when it was sent for carbon dating, it showed the wood came from a time between 660 and 780 AD, putting it in the Saxon period.

Richard Mortimer from Cambridgeshire Archaeology was the project leader on the dig in the summer.

He said: "We don't know where people would have been in that time. That area of Wisbech was supposed to have been empty until the Normans turned up and built Wisbech Castle. This find was from 400 years earlier."

The wood was found in a rubbish dump in a ditch or terrace two-and-a-half metres below ground. The find hints at early occupation in the centre of Wisbech.

Dave Brown and Tom Phillips were the two archaeologists on site over the course of the week. The dig site was in the small courtyard area by the entrance to the library and they could only open a trench that was 4m by 3m due to the small size of the area.

The first find was a cellar wall estimated to be from the 19th Century. It had been built on top of the base of an earlier wall, which could have been from a Georgian house built at the end of the 18th or start of the 19th Century.

By the time they'd reached two metres below ground level, they were finding late Medieval soil layers, backed up by a few finds of pottery.

In the same area as the Saxon wood, the archaeologists found pottery fragments dating back to the early Medieval period, around the 11th Century.

It is thought the layers of silt in the trench could represent periods of flooding.

Flooding was a major issue in Medieval times. A massive flood was recorded in 1236.

It was described in the Flores Historiarum: "The waves of the sea flooded in, transgressing their accustomed limits, so that in the confines of that same sea, and in the marsh, as at Wisbech and in similar small places, small boats, herds and also a great multitude of men perished."

It is thought the flood could have been responsible for the destruction of the original Wisbech Castle, built in 1086 on the orders of William the Conqueror.

Mr Phillips said: "It would be great if we could tie this flood to the flood layers discovered recently, although we can't confirm this at present."