Bought this Orange P7 on ebay a few weeks ago, and was apparently all fine until I realised I had to drop the seat as was too high for me.
Unbeknown to me, or apparently the seller, the alloy seat post is properly corroded into the P7's steel tubing.
I have tried all known methods: basic turning of the post impossible; more forcefull approach with a vice also failed, even my bike shop was unable to make it move even half a mm; leave soaking in decent penetrating oil; pour in Coke plugging all holes with plasticine, use combo of heat and cold, general swearing and shouting, more brute force attempts etc.
Only thing didn't try was ammonia or Caustic Soda, although I did buy a bottle mostly because there is simply no cavity/space for any liquids to penetrate , so decided to leave these till the last stage which is cutting.
And that's where I am now, started off OK, but what you see in the photos literally took 8 hours of sawing and filing just to be able to peel back a few strips from the top. The real mare is that the post is about 5" down into the frame, so regular saw blades proving hard to get and reach the posts end.
I think in time, with more gentle sawing, open up a few more cavities, I can try the Coke and Caustic liquids again. If that fails then it's back to just more time consuming sawing and poking.
A few photographs to show the pain: