In its annual survey of High Street travel agents, Columbus Direct claims to have uncovered a litany of cases of insurance mis-selling.
In one case, it alleges a woman was unable to remain in Spain with her dying husband as his insurance policy would not pay for her extended stay.
A spokesman for the travel insurer said it had uncovered other instances where people had been sold inadequate insurance that did not cover pre-existing medical conditions.
Another key finding from the survey is that more than a quarter of travel insurers allegedly concealed the true cost of insurance in the price of their holidays.
Surprisingly, this hidden insurance can cost up to 200% more than a comparable product sold by a direct provider. The survey also alleges that one in ten travel agents is flouting a ban on offering customers discounts if they agree to purchase insurance with their holiday.
Columbus has been monitoring the sale of travel insurance for the past five years and claims to have found no improvement in the way cover is sold.
Other findings from the survey are; only four per cent of travel agents asked customers whether they intended to take part in sports activities while on holiday. And only eight per cent asked about pre-existing medical conditions which can invalidate subsequent claims.
A worrying minority of travel agents simply failed to encourage buyers to read the small print of policies, despite an ABI code of conduct.
A Columbus spokesman said it hoped the survey would raise awareness: "Travel agents should either sell insurance well or not at all. We will continue to raise awareness of badly-sold insurance, until proper controls are put in place to ensure customers are not put at risk unknowingly."