About 14,000 ex-miners have submitted compensation claims for respiratory illness to the government this week as the deadline for submitting claims looms, said a report.
The Department of Trade and Industry (DTI) said the sudden rise in claims followed a publicity about the 31 March deadline.
According to the report, 516,000 claims have been registers for chest diseases linked to working in the pits.
In February 2004, Capita announced it had won a DTI contract from Aon to administer all miners' personal liability claims relating to certain health conditions caused by working in British Coal mines.
It is six years since a legal ruling allowed miners and relatives to claim compensation for work-related diseases.
The government has paid out £2bn in compensation since 1998, but Capita said miners' compensation claims were the government's largest uncapped liability, estimated at £7bn.
Trade union law firm Thompsons said it was receiving 300 calls a day and had registered 4,000 claims so far.
