Thanks very much for taking the time to reply.

"Not unless the current radiators are shot - which they *may* be if
the
system has been run for years without inhibitor, so that they have
rusted
inside. In this case, fitting a new boiler - which will almost
certainly use
a non-vented (pressurised) system - the extra pressure may just be the
last
straw which may cause them to start leaking. On the other hand, they
may be
perfectly ok. " - Is there a test that can be performed to check for
the integrity of the radiators/pipework?

Any recommendations on brands of boilers?

Thanks again