Sinks - amazingly neither the IEE regs nor the On-site Guide specifies any restriction, but there is new guidance in the IEE publication 'Electrician's guide to the Building Regs' section 5.2, page 56 onwards.
It suggests no sockets within 300mm of sink edge. The picture on page
57 shows this as a horizontal distance (ie not a diagonal). Centre line of sockets to be 150mm above work tops.
Something similar for the cooker switch is shown in the picture, but the picture is not fully compatible with the text rules in 5.2.2 . At any rate switches should not be located so that you have to reach across the appliance to use them.
There's other guidane which it might be worth your checking out, or if you're kucky someone else will be along soon with it all....
Sorry - no experience of gas, never having lived anywhere with it. However perhaps the 300mm in the Electricians Guide picture could be a good starting point? Have you tried seeing how near a gas hob you can put your hand before it fries?
I usually fit electric cooker switches around 100mm to the left or right, but electric cookers don't have the gas flame problem. Perhaps the possibility that the cook may need to turn off the cooker in an emergency & need to stretch across a cookpot which has caught fire, or is spraying steam in all directions, is a consideration.
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