An RCD trip would suggest an earth leakage fault, this is most commonly attributed to the heating element.
You may find the interior part of the element has started to fail, and as it heats up its resulting in current reaching the outer element case which is grounded.
Does the fault occure only when using the fan over, or the grill?
The fact its after 10 minutes would suggest its the element in my view, as the fault is caused by the heating up of the element. Its very difficult to prove these faults, as the short is happening when the element is red hot, but when your looking at £30 for a element its the cheapest and most effective approach to fault finding (swap the part out).
Another way to test its the element is leave the oven on for an hour just on fan (temp set to 0), so the element doesnt come on, if it doesnt trip, then turn the temp to 200 and see if it trips in the next 15 minutes.
How did you get on with the cooker?
There is a power regulator in the control panel.
I wouldnt worry about the voltage to the element, to confirm you have had oven running with the fan element on for 2 hours and its not tripped?
I havent heard back from you in the last day or so, and just wanted to check if you still require assistance?
Glad it is back working again, if the fault does reoccur, I would look to swap out the element.
Sorry to hear your having difficulties with the website.
Appreciate if you can rate the service received so I may close the case.