If the item is showing as delivered on the courier's or Royal Mail website
And
More than 48 hours have passed since delivery was recorded on the relevant website
Then
Contact Ebay Customer services and ask them if they can check the tracking and release your payment.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)