Who ever told you you need to cross bond your boiler in 10mm is quite frankly an idiot.. In fact irrespective of the size of cable he told you to use he is still an idiot for telling you to cross bond it.. Half of what people think you needed to bond was for the most part Myth and Legend.. All this having to bond sinks, draining boards, boilers and all manner of other stuff hasn't been needed for years, I can only cast my mind back as far as the mid - late 90's it certainly wasn't required from 2000 onwards there may have been something back in the late 80's possibly early 90's but thats getting on for 20 years.
Evening JP. Yep, think those are pretty much the recommended in the on-site guide mate. Happy days! Cheers Fats
I personally would always fit a 16a circuit for the oven as you can soon overload a ring if kettle oven and a few other items are run at once. As far as the earth bonding goes I still favour doing it anyway as have found loads of faulty rcd in the past so would rather have bonding there as a back up