Chunks of road surface crumbled away from the raised bridge section when it was being tested before an official opening ceremony by Princess Anne on Monday.

The Borough of Poole had initially dismissed the problems as small glitches but now the council has confirmed that “defective” sections have been found on both lifting leaves of the £37m bridge.

Workers found the rubble on the Hamworthy side of the bridge after it lowered and then took up more loose material to leave a 20m by 7m area to be relaid.

An investigation is now underway to determine how much of the road surface needs to be replaced.

The bridge had been due to open to traffic on 27 February but will continue to be closed to traffic while contractors investigate the blacktop.

Poole’s strategic director Jim Bright said: “After an initial inspection last week revealed an issue with a small section of the road surfacing, the bridge was left raised all night on both Saturday and Sunday.

“At some point between 7.30pm on Sunday and 7am on Monday a small area of defective surfacing came away from the top section of one lifting leaf.

“This incident did not present a hazard and subsequently the contractor has removed a section of the road surface around the area affected.”