Royal & SunAlliance (R&SA) and Allianz Cornhill could face claims up to £20m following the collapse of the Gerrards Cross tunnel where a Tesco store was being built.

R&SA is understood to be the main insurer for Tesco for liability and contract works for the project, while Allianz Cornhill Engineering provides contracts works cover to contractor Jackson Civil Engineering.

The Health & Safety Executive is investigating the collapse of the tunnel onto the Birmingham Snow Hill to London line run by Chiltern Railways at the end of June.

In addition to material damage claims, a substantial business interruption claim from Network Rail for disruption to the Chiltern Railways link is expected.

Loss adjuster Cunningham Lindsey is representing Network Rail in preparing its claim.

An R&SA spokeswoman played down the potential claim saying: "We're disbelieving about [the amount of the claim], although I would emphasise that whatever the cost, we have significant reinsurance in place."

Allianz Cornhill, Tesco and Jackson declined to comment.