Discussion: This is why

I like riding bikes.
You can train properly hard without battering your legs to bits and then having to wait until they recover for the next hard session, by which time the effect of the last one has gone.
You can make progress.
I think you could strike a good balance doing your hard aerobic work on a bike and longer less destructive endurance running to keep the resilience in your legs.

Good thinking - maybe I should dust off the bike and try some - I do enjoy it once I'm out there, just the faff of getting ready puts me off!
There are plenty of hills round here to do intervals on...

You can't do that.... I'm just about to cannibalise it for spare parts :-)

I can use the mountain bike - has 2 wheels and goes up hills :-)

And definitely much better training effort seeing as it's so heavy

;-)

I think what Sarah is meaning to say is - Buy yourself a nice new bike Jon

Actually she's saying buy yourself two new bikes: one road bike, one mountain bike.
You definitely need both where you live ;-)

you are forgetting the cyclocross bike Charlie

And the track bike...

Maybe best remind yourself how to ride first :-)