the absoulute cheapest way would be to walk. or cycle. you could take a train or bus
Blackpool is nowhere near London.
hitch a lift, or travel with a drug dealer! There are lots!
On foot
from where
It usually takes about 5 hours to travel from Blackpool to London under good road conditions (i.e no traffic jams on the way or stop-offs).
Blackpool England is not a capital city, London is the Capital.
Train
Roughly 240 miles. See related links for driving directions.239 miles from Blackpool to London Marble Arch
About 200 miles
Cycle or hitch-hike
When I was in the service, one way was intercity bus ( I don' t remember what they call it in Great Britain) but, for me, it was and I assume still is the cheapest way to 'get about,' as they say.