We've got a small wall clock that we need looking at. Does anybody know of anywhere in the SE1 or commutable area? The issue appears to be with some corrosion of the battery mechanism, or possibly a battery leak melting the device.
Try SDV Jewelers at !00 Lower Marsh, next to Boots the chemist. Most of their work is done within a day or two, sometimes whilst you wait.
If it is corrosion as you suspect and is a quartz battery driven mechanism then it might not be repairable and may require new works which are relatively cheap.
They will give you a quote free of charge.
I am an extremely satisfied customer and have used them for everything from pocket watches to a long case clock, batteries and watch straps etc.
Try them, it will cost you nothing for a quote.