If they are proper floor boards then that's great (and cheap). Don't varnish them yourself. Get a floor finisher to sand(if necessary) and laquer them for you. Won't cost a fortune but well worth it. It is much better than varnishing, even with the Ronseal hard floor varnish.
On another note, it will be an ideal time to check out your pies and wiring under the old flooring and make any repairs or renew any you think is on the way out. Nothing worse than having to rip up your new floor in a year or two.