we have a cloakroom where the countertop is very narrow, just 23 cm in width. we want a luxury looking basin but there are hardly any that are of that size. we are thinking of getting a countertop basin which will overhang the top and the one we like has width of 35 cm. will it look odd? the basin will match the rest of the cloakroom and is exquisite.

Jonathan is quite right in that it would be expensive as you're basically looking at starting again with your kitchen design and it looks like granite worktops that would need replacing, probably easier to rip it all out and start again, you might be able to re use some of the existing units with some clever design.

You’re bound to get more water splashes on the top because the bowl is so small. Constant water splashes will ruin the worktop especially if they are not wiped up immediately. You will have to find something like a blunt knife/screwdriver, wrap cloth around it to wipe around the bottom of the basin where it joins the top to clean it to enable you to get right into the edge but I wouldn’t image you would need to do that too regularly.

You can get worktops made to any thickness, granite and quartz usually comes in 20 or 30mm thicknesses but it can be made to any thickness and with different edge profiles, the underneath is packed with mdf and all the edges are made thicker. You can also get laminate worktops made extra thick by a laminate fabricator [google for a local fabricator], they would get/make the base board [chipboard] to your thickness and then bond the laminate sheet to the tops and sides [square edged]. There's also concrete worktops which can be cast to any thickness, copper and stainless steel worktops can also be made to any thickness. Also real wooden worktops can be made to look thicker by a decent kitchen fitter or carpenter.