The Building Regulations require that you have a condensing boiler installed unless you score 1000 points on an exemption assessment. This has presumably not been done, or you would have seen a copy. There is no obvious practical reason why you shouldn't have a condensing boiler since the condensate drainage and flue plume dispersal are not going to be problems. The installer's quote must be assumed to be for a condensing boiler, since that is what the Building Regulations require.