I'm going for beers that are no longer available in their original form and as far as Boddies and Bass go it's back to the seventies.
Brakspear Bitter - the Wychwood one is nothing like the Henley original.
King & Barnes Old - some of the current Horsham micros have made a good job of recreating this.
Boddington's Bitter - It was never the same after it escaped from Manchester and the NW.
Pitfield Street Dark Star - a bit of mischief!
Draught Bass - It was ruined in the early eighties and is now just a poor variation on Pedigree.
I could add the two Young's bitters, Marston's Owd Roger, Lees Moonraker, Ruddles County, Gibbs Mew Bishop's Tipple and many more but... Oh! I just have.