Distance between high level oven and hob?

Check the manufacturer's information for the hob, this should include clearance zones. The building regulations themselves only include specific dimensions in relation to the distance between hobs and extractors (part F - ventilation), nothing for distance between hobs and ovens. If your oven is housed in a tall unit (which I assume it is), then watch out for any requirements relating to walls or adjacent vertical surfaces i.e the side of the tall unit. The minimum distance permitted could be quite low, but in reality would advise a minimum of 300mm to allow space for pan handles etc.

Generally id give about 60 mm as a minimum, but havnt fitted many that close as most people want useable surface next to an eye level oven. I would try and get it as far away as possible for aesthetic reason as well. Most regs and guidlines refer to extractor height rather the distance to the side

I'd revert back to the manufacturers guides

There is a minimum of 650 mm height distance by regulations, also you can refer to the manual of the hob/oven.