No STA, Deposit not returned

Tenancy Deposits

Asking for a friend (really!)

A friend rented a room in a shared house with the owner.
No paper contact, just a verbal agreement.
A deposit of £550 was taken.

After a couple of weeks it became very obvious the tenancy was not working, as amongst other issues, the owner came into the his bedroom on a daily basis and unplugged all IT equipment.
(Having been asked not to even enter the room)

After 3 weeks my friend left.
He now want his deposit back
The landlord is not responding to email requests.

Does the ex tenant (or the Landlord) have a leg to stand on ?
In the absence of a STA can this be taken to the Deposits Ombudsman ?

(As a landlord for over 40 years I'm appalled that he agreed to this, but there you are)