Get the installation checked, as gas back boilers are meant to be fitted with gas fires, if the boiler or fire has been altered in anyway it could be dangerous. You cannot use a back boiler without the correct fire front being in place.
Back boilers don't really come with much choice of fire, normally just one fire will fit. If you're licky you might have a choice of 2 or 3 fires.
If the back boiler is old, you may struggle to find a fire to fit (this might be why they have fitted a electric fire to it)
Could you not have a new boiler installed, and have a traditional looking gas fire installed, or have a wood burning / open fire ?