Seat post advice needed for carrera subway 2

[danoffroad]

I have a Carrera Subway 2 too and I have made lots of upgrades. I still got the tyres but I use them only in the summer months. In the winder I use some 26 x 2.0 with plenty of grip.

Upgrades are:
Saddle for a Brooks Flyer.
Stem - probably the best upgrade I made so far.
Wheels - got two good hand made Mavic wheels.
Crankset - upgraded the crankset as the old one broke.
Pedals - for SPD Shimano pedals - old pedals were poor.

Very happy with the bike now. Fine for what I need.

You couldn't help me with this issue manonabike could you please ?
The seat on my Carrera Subway 2 became all lose and now it won't sit tight in the seats hole. I've enclosed some photos for guidance. There's a washer at the bottom of the hole and the metal thing in the hole that moves up and down that I can't get out, where the stem fits in.

 

[Pat "5mph"]

Mod Note:
This OP has been moved from a similar, older thread that was in the beginners section.

 

[Kingfisher101]

I've never seen anything like this seat spring thing. Looks strange. I think I'd take it to Halfords after all its one of their bikes. The seatpost looks like a bodge job?

 

[Drago]

If I'm interpreting the pictures correctly, that's one of those awful sprung seat posts. Looks as it its come apart and the outer sleeve is stuck down in the seat tube?