It's also a bit of a farce. The largest party in government (Labour) has repeatedly said no, this is stupid, it's too expensive, it's not worth it. Their junior partners, however, want it. And then one of the "fiscally responsible" opposition parties signaled that they would support the tunnel. So to avoid the junior partners splitting off and agreeing on a budget with the opposition, Labour now supports the tunnel too.

No doubt it will cost a ton and be derided as a boondoggle/used as justification for austerity by the conservative wing which indirectly made it happen.