The Harrison & Harrison organ was installed in 1909. It has four manuals and fifty speaking stops with space for an additional reed in the Solo Box. Comprising 2,715 pipes it is believed to be virtually unique in that it has had no modification since installation. Most instruments of this size are in cathedrals and will have had several rebuilds to meet modern tastes in voicing. The rich tone with particularly fine reeds and a reliance on solid 8' stops is typical of the best of the Edwardian age.
The console is set back behind the Chancel choir stalls and in this position the organist can neither see nor hear the priest or congregation in the Nave. The organ is blown by a small induction motor in a chamber under the churchyard which replaced a huge DC motor operating up to the 1950s.
Sadly, the instrument is not maintained due to impending major work and roughly 50% of the instrument is now unusable either in part or totally. There are many leaks, the action is slow, a lot of the couplers do not work, many stops are inoperable and the tuning is interesting.
Plans are under way to have the instrument restored to full working order.
A day conference organised by the British Institute for Organ Studies took place on Saturday 22nd May 2010 to discuss the relative merits of replacing the pneumatic action with an electronic system. The unanimous conclusion of the conference was this instrument was too important and should therefore be restored as it was built. The total cost of this including endowment, will be in excess of £1,000,000 and is part of a wider project to make St Mary's more accessible as an educational and concert venue.