Whether the engineer is from british gas or not; we all take the same training, have the same qualifications and experiance to be accepted on to the CORGI register, and most of us are Ex british gas who have seen the light and no how much of a rip off and uncaring they are.
Any-ways to answer you're question : YES It can be done but it is a lot of work and very expensive to lay gas pipework through concrete. That is prob why he did not recomend it. Concrete actually attacks pipe work so therefore it has to be very well protected against attack. The best way and safest way is to cut a channel in the concrete and have a joiner line it out and fit a removable lid / top to it and then you can safley install the gas pipework without any fear of errosion. Or you can use GRP pipework but that still will need wrapping and any joints will need to be very well protected .and it will have to pass a tightness test before it is wrapred and the joints protected + coverd over and again pass a tightness test afterwards again. As you can imagine loads of ���s...
Also do you relise that a flueless gas fire will need permanent ventialtion installing that means you will have to have holes cut in your external walls and air vents put in for it to opperate safely and it can get quite drafty in winter. You also need to have a room volume of at least 5 cubic meter in the room of installation and if there is a door to an adjoining room that has an extractor fan or cooker fan in it then this could well be a big permantly open vent in you're living room !!!
So just a few thing to consider before going ahead that you may or may not have known about.