When administering an estate it is the executors responsibility to collect in the assets and to discharge all liabilities.
Often, smaller assets can be forgotten and remain unclaimed, however when added together could result in a meaningful sum not being collected in and distributed between the beneficiaries.
Assets which can often be overlooked are those few pounds in premium bonds (held from a time when it was possible to buy bonds at a pound a time), membership subscriptions, together with digital or online accounts we hold e.g National Lottery, PayPal and as brought to our attention in the linked article, Oyster Card.
The amount amassed by TfL is of course not just a result of unclaimed balances held on deceased accounts, but a portion could well be, and is a pertinent reminder to check all 'accounts' when administering an estate.
Individuals can help their executors in the discharge of their duties by keeping an up to date record of the names of organisations where they hold accounts, so that it is easy for the executors to identify who they need to contact.
Link to related article: www.bbc.co.uk/news/uk-england-london-50304437