Do we sell or apply for planning permission?

[changer121]

My dh has inherited his parents house after sadly loosing them both.
It's a large plot in the Home Counties that will be renovated/knocked down etc by whoever buys it as it's very unmodernised.
Would it be worth us going for outlying planning permission for a larger house on the plot or is it not financially viable
To do this and we should just sell now?
It's a 3 bed detached but properties in the road have been made into 5/6 beds etc with basements but we are unsure if it's worth it ?

Consider if the plot is large enough for a second house to be built there, maybe also ask local estate agents opinions, get them to give potential valuations for a variety of options?

There would be not point going for outline PP for a replacement. The principle of a dwelling is already established. The Council would probably want so many details you might as well go direct to full PP.