Brits who are unaware of the value of goods stashed in their attic could face problems if they ever need to claim for them, a leading insurer has warned.

Homeowners need to get their potential treasures valued and then ensure they are covered under the single item limit on their insurance policy, warns Saga Home Insurance. Most insurers offer cover between £1,000 and £2,500. Items which are worth more must be listed separately on the policy.

But Saga Home Insurance is also encouraging people to sift through forgotten boxes in their attics to see if they are unwittingly sitting on a potential goldmine.

Decorative arts from the 1950s, 60s and 70s, pop art and classic film posters are now becoming collectors items – a 1967 film poster advertising ‘Don’t Look Back’, starring Bob Dylan and Joan Baez can fetch up to £500.

Memorabilia in good condition such as Thunderbirds models can bring in between £600 and £800.

Andrew Goodsell, chief executive, Saga, comments: "Often the most unexpected items turn out to be valuable. If your possessions are undervalued, you could find that you receive only a fraction of their worth in the event of theft or damage."

But Saga is also recommending that valuable items are given an identifying mark such as the owner's postcode, or if this would devalue them, colour photographs should be taken, along with measurements and notes of any scratches or dents to facilitate insurance claims in case of damage or theft.