Generally the dishwasher spaces are around 61cm wide, but the plumbing for the sink and the isolation valves are in the way, certainly on ours and others we know of. The valves should be accessible (away from the back of the D/W - ideally in the sink unit) to turn the water off in case of emergency (ie water leaks). However, be careful, as this will be a very difficult error to correct. It would probably mean changing the sink position, which affects the worktop and so on. Also to alter the valves may mean tiles / walls being chopped out, so a very messy job.
The compromise, as sugarmummy points out, is to install a 45cm D/W and maybe have a pull out towel rail alongside it, or get Roda to build a tray space unit to fill the gap (bearing in mind it is their mistake), which can be removed for access to the valves.
Be aware that Roda are trying to make out you are the only ones with these problems, but, as we are finding out, many of us have the same errors in our properties. We all make mistakes, but Roda are refusing to correct some of theirs, usually the ones that cost them a lot of money to put right.