Around 671,000 young adults are sitting on unclaimed pots of cash worth more than £2,000 on average, according to HM Revenue and Customs (HMRC).

The revenue body is reminding 18 to 22-year-olds with unclaimed child trust funds (CTFs) about their windfalls – with the average savings pot worth £2,212.

CTFs were set up for children born between September 1, 2002 and January 2, 2011.

Many children got around £250 each from the state at the time their CTF was started, while those from low-income families or in local authority care received an additional £250.

Young people can take control of their account at 16 and withdraw funds when they turn 18.

But some young adults may have forgotten about their accounts or be unaware one was set up on their behalf.

The savings are held in banks, building societies or other saving providers. The money stays in the account until it is withdrawn or re-invested.

Angela MacDonald, HMRC’s second permanent secretary and deputy chief executive, said: “Thousands of child trust fund accounts are sitting unclaimed – we want to reunite young people with their money and we’re making the process as simple as possible.

“You don’t need to pay anyone to find your child trust fund for you, locate yours today by searching ‘find your child trust fund’ on gov.uk.”

If teenagers or their parents and guardians already know who their provider is, they can contact them directly.

If they do not know where their account is, they can use an online tool on gov.uk.

People will need their national insurance number and their date of birth to access the information.

The CTF scheme closed in January 2011 and was replaced with Junior Isas.

HMRC said third-party agents are advertising their services offering to search for CTFs, but people using them face potential charges, which could include a portion of the value of the savings account.

Using an agent can significantly reduce the amount received, HMRC said.