Engineers from Hertfordshire County Council have warned that a further giant hole could open up on a street in St Albans affected by a sinkhole earlier this month.

The seven metre deep hole appeared in the early hours of 1 October, causing families to be evacuated from their homes.

A Geotechnology microgravity survey commissioned by the council took place on the road and footpath in Fontmell Close and Bridle Close.

It revealed the collapse occurred within the boundary of a backfilled clay pit which had been excavated in the 19th century for brickmaking and backfilled with waste from the area.

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Experts said the 'most likely' explanation for the collapse was chalk excavation in the bedrock beneath the clay.

However, while the hole has now been filled with 48 lorry-loads of foamed concrete engineers are now warning a "number of anomalies" have been identified which could lead to a larger collapse, possibly up to three times the size of the previous sinkhole.

Deputy director of environment for the council, Rob Smith, said: "Since we received the report we have met with residents to discuss its findings and to help them understand the contents of the report.

"We appreciate this is upsetting news and are continuing to work together to determine the next steps. The safety of residents remains our priority.

"We are keen to enable people in the area to be able to come and go from their homes more easily and are looking to create a more permanent temporary access road."

(LM/CD)