Hi Highlander,
I also have a £50 note & just checked Bank of England,s website. Only certain notes have been withdrawn. see below.
£50 banknotes carrying the portrait of Sir John Houblon were withdrawn from circulation on 30 April 2014.
Only the £50 banknote featuring Matthew Boulton and James Watt, which was introduced in November 2011, now holds legal tender status.
Most banks and building societies will continue to Houblon £50 note backaccept them for deposit to customer accounts; however, agreeing to exchange the notes is at the discretion of individual institutions.
Barclays, RBS, NatWest, Ulster Bank and the Post Office have all agreed to exchange Houblon £50 notes for members of the public - up to the value of £200 - until 30 October 2014.
The Bank of England will continue to exchange Houblon £50 notes, as it would for any other Bank of England note which no longer has legal tender status.