Chart found here 4 mm² 17.5–37 amps depending on installation methods, flat twin and earth is made as a 90°C version as well as 70°C, but there are no charts I can find for it, but for other multicore cables we see 30–49 amps, so I would say no real problem on a 32 amp MCB/RCBO.
The whole idea is the protective device will open before the cable is damaged, with a short circuit that will be the case, and with the oven is rated at 9.6A/2.2kw it is unlikely to have a load over 17.5 amp for an extended time, so in real terms not a problem.
Where the problem lies, is when the oven is changed for a larger unit. We know the MCB should protect the cable, and in your case if the unit can draw over the rated amps of the cable it will not protect the cable if the oven is swapped.
The other question is what is needed to protect the oven its self? Often internal wires are not even 4 mm² and for any item not plugged in, the manufacturer can stipulate maximum supply size, often they don't, but clearly there must be a limit, would not be safe on a 100 amp supply. So we look at tradition, and traditionally a cooker has a 32 amp supply, so in the main we would supply any cooker with a 32 amp supply unless the manufacturer says otherwise.
So I would continue as you are, but get a replacement of correct make and size for the consumer unit and next time you get any other electrical work done, get it changed at the same time. But no hurry, until oven changed there is unlikely to be a problem.
