Hi, this is a common concern with clients. So long as the cable is double sheathed ie.twin and earth (the grey stuff) and on an RCD protected circuit then the regulations state it does not need to be the required 50mm minimum depth. Due to improved safety measures along with time and cost metal containment within domestic installations is very rarely ever done nowadays except for very special circumstances.

As long as the cables are RCD protected then no need for any capping etc in the first place. And as you have had it rewired I'm guessing they are. So it's ok.

It would generally be regarded as good practice especially where multiple trades are working on site and there is risk of cables being damaged/severed. It can save cost, hassle and downtime if such measures are practiced.

Well this is going to be controversial and I can already hear the opposition, because 1st of all the regs are not statutory so it can't be illegal.
2nd the cables are covered in trunking/capping as much to hold the cables in place and protect from other trades.
Most of us have been told as apprentices to always cover the cables in capping and we do without thinking about why we do it.
So it is safe and it isn't illegal - yes as long as it is covered in something that protects it then it is safe from mechanical damage, it might not be best practice.

Agree with most of what has been said. It is more a case of good practise rather than illegal as there is nothing legal about the regs! The installation either complies or it doesn't . RCD protection is the key factor which if it was a rewire hopefully you have. One point I would add is that if the cable is housed in a protective cover be it plastic or metal it makes the next rewire that little bit easier.