There are two aircraft and normally two flights a day.
In peak times, the B767 may be utilised more.
The B767 config for BA is Club Europe 2-2-2, Euro Traveller 2-3-2. Where the cabin starts depends on the Club loads but can go down to row 25, and if you prefer leather to cloth seats book forward of row 25 as the back section is cloth seats.
The A320 config is either 2-3 or 2-2 in Club (depending on load) and in Eurotraveller is 3-3.
BA have before substituted the route with a B757 but this is very rare.
If you are booked in Euro Traveller, try to get the front row of the EuroTraveller cabin on the left of the aircraft (seats A & C) as sometimes you still get club config sized seats in this row.