Yes - it's the second deepest lock in Britain. Tuel Lane on the Rochdale Canal is slightly deeper, and similarly was created by combining two locks to get the restored canal under a road. Tuel Lane is keeper-operated though!
Two more pictures from last week. I didn't set out to record the depth so these are incidental - from below the lock - under the bridge from below, and from above - noting the cement mixer in the background which is on top of the canal below the lock.
As someone who's done a fair old number of locks (but not Tuel Lane), the extra 7 foot or so on top of Tardbigge Top Lock at 12 feet which I have been through quite a number of times isn't all that noticed - perhaps because Bath Deep lock is wider too, so scaled up from Tardbigge rather than distorted.
The steps seen in the first picture are a massive help. Had the lock been directly against the bridge, with crew obliged to cross the road to get on / off the boat, you would have a real operationally difficult structure. Not sure what the status is on Tuel Lane.
If you want a deeper lock take a look at
Ardncrusha on the Shannon Navigation, again a late construction to replace a a canal section when the HydroElecctric scheme was built there in 1929.