This is the overall kitchen - faces south west, and has a diner behind it.

This is the joint failure. Apparently even sealed joints shouldn't be this close to a sink, but even a joint going at right angles would still be fairly close.

Thank you for sharing your thoughts. Yes, the install is definitely poor and the back piece of the U should have gone all the way across, with better joints and everything sealed, and the tap through a sink not through wood. It's hard to know how to proceed. The worktops match the splashbacks, the floor and the dining table nicely, but real wood is definitely a no (too much maintenance) and my confidence in laminate has fallen. I can't move the sink centrally on the U without messing up the drawers to the right. Would these splashbacks really have to come out with any worktop change, or only something that changes the worktop thickness (from 38mm)? Is 'water resistant' laminate a significant improvement from regular laminate? If I changed the material, what colour would work best with the wood and these cabinets, assume some kind of grey or cream? If I need to change the splashbacks, would a small overlap of worktop material and painted wall above be best? When changing the sink, should I go for a combined sink drainer with tap on the middle or a single bowl with tap centred on the bowl and no draining board?

My advice for the sink would alway be to choose one with a double bowl and side drainer. Having the second smaller bowl to rinse plates and pour out leftover liquids from cups and so on is so handy. And a single mixer tap with pull out function is great for cleaning the sink itself.

You could consider an insurance claim. Ideally to fit the new worktop the splashbacks need to be removed, this will probably damage the walls so its quite a big job. You may find a fitter who is prepared to work with the splashbacks in place, but the sink run would have to be cut short to fit in between the splashbacks and then the gap filled with silicon. How to get the worktop in position may also mean removing some wall units as well. then for the 2 side worktops being able to slide under the splashback and making a decent job of the masons mitre, keeping an even overhang to the doors etc, not a job i would of undertaken when i was fitting.

You mention water resistant laminate, if you mean compact laminate, the max thickness is 20mm so there'll be a gap. If you mean laminate but made with 'green' chipboard, it still needs sealing and if its constantly subjected to moisture it will still blow.

I'd suggest a new worktop in a stone/abstact pattern colour as you have a modern door style, make sure it's a bullnose and not these edged worktops [i've seen these fail around sink area], get rid of the splashbacks and fit some metro tiles in a brick pattern, also get rid of the windowsill so that is also tiled instead of that gap you have under the sill. Reason for tiling is that if the splashbacks have been stuck on with silicon, even if the wall isn't damaged any silicon may affect the new paint.

For the sink, you mention that you want to wash oven trays, so for a bigger bowl opt for a single bowl with a right hand draining board as well, looks like its a 600 sink base in the pics so there's plenty of choice, personnally i'd have a 1.5 bowl though as Betty says, also opt for a composite/granite [as below] so you can just drop the sink in place on a bed of silicon beading, stainless steel would ideally need the clips underneath [there are a few push in stainless sinks though with spring clips].