Residents are being warned to be on their guard against the conmen - and urged to look out for elderly and vulnerable relatives and neighbours.

The crooks often pretend to be from utility companies or local authorities to gain access to their victim's home.

Others claim to be ex-offenders selling products as part of a probation scheme - the Probation Service does not run any initiatives of this nature.

Workmen calling at the door should never be employed - always look for a reputable local firm, and seek recommendations where possible (local councils and charities can often assist with approved contractors).

Even a lost ball or pet, or a need to use the toilet can be a ruse to gain access to a home and someone's valuables or savings.

Crime prevention experts offer a series of tips to help people protect themselves against the conmen:

• Get into the habit of checking who is at the door - if you're not expecting anyone, consider whether you should answer the door at all
• Use a door viewer (spy hole) or shout through the letterbox
• Consider fitting one of the many doorbell type cameras available - some providers charge a monthly fee for storing images, so do some research to establish the best option
• If you can, go to a window and deal with visitors there - it's a lot easier to dismiss unwanted callers from the safety of your home
• If you do decide to open the door, use the chain or a door bar
• Don't keep savings or other large amounts of money in your home - use a bank or building society

Cleveland Police Crime Prevention Officer Gerry McBride said: "Bogus callers come in all shapes, ages and sizes, so we all need to be on our guard, and looking out for each other.

"They often work in pairs, so while one is distracting you the other is searching through your belongings and looking to steal cash and other valuables.

"Remember, ‘lock, chain, check', and if you're not sure - don't open the door!"

Councillor Dorothy Davison, Middlesbrough Council's Executive member for Adult Social Care and Public Health, said: "Sadly there will always be an unscrupulous minority who prey on the vulnerable and the elderly.

"It's down to all of us to make life as difficult as possible for them - look out for your relatives, friends and neighbours, and report any suspicious activity to the police immediately."

• Anyone with information about a crime should contact the police on 101 or CrimeStoppers on 0800 555111.

• For the latest local updates and information, visit middlesbrough.gov.uk/covid19

For information on local help and support, visit Help Boro at www.middlesbrough.gov.uk/helpboro or call Middlesbrough Council's support line 01642 729777

The latest advice from Government and Public Health England can be found at https://www.gov.uk/coronavirus