You could try hiding it in a jar of coffee.
One word of warning though, the tunnel is better protected than any other route.
Airports place dogs by the luggage carousels and the passport control, I have managed to walk past one while carrying weed in my baccy.I think that I read somewhere that explosives dogs can't sniff out drugs and drugs dogs are no good for looking for C4.
Belgium to any of the major British ports is the best chance.