I think you will find that in recent years side facing seats for travel are not allowed ----to confirm this, go to any MOT test station and ask-------when you say 'new' I presume you mean 'new'.
We have an older motorhome with side facing seats but these are legal.
If that is a new vehicle side facing lap belts are illegal in the eu.
at least that is how I read the gov website.they have the number of seats with 3 point belts in the log book.
2008 to 2012 a bit dodgy on the law
before 2007 no belts required in the rear but if fitted they must be used.
I spent over 12 months trying to find out the seat belt laws mainly as we had plans to take our grandchilren with us to help out over the summer holidays for the working parents.
This prevented us buying the motorhome I/we originaly wanted that was old [historic] with no rear belts.
It is a total black hole from 2007 to i think its 2012 [stored somewhere on this pile of junk hp call a computer]
this has now vanished from the gov.uk website.
Even family members in the police are unsure.
Mine is a 2008 with seating for 7 and only four 3 point seat belts, best that came up was over 4 " are you likley to cause or have caused an injury, not, not wearing a seatbelt" though never heard of such a case.
It is very clear on children, if they are not in the correct seat they can not travel with the exception of an emergency over a very short distance [the school run is not an emergency]
Children under 135cms and up to 12 years of age have their own eu law. this is also changing---
From Dec 2016 they must be in a high backed booster seat sutible for their age/weight, booster pads are banned so now we have to go and buy another seat or two to clutter up things.
for those interested you have to go to the start then read the amendments. it is a long process and you need to look for motor vehicle not being a car if my memory is right.
I was only looking for child restraints when I trudged through it all but other bits stick in your mind. http://www.legislation.gov.uk/uksi/1991/1255/made