Demand is certainly keeping the prices up.
I was recently bidding on an MG Metro engine and gearbox (with no ancillaries) and dropped out when it got to £900 as there was another standard A+ 1275 engine auction ending an hour later plus another MG Metro available as a classified listing and I thought it better to get an alternative at a decent price rather than get caught in a bidding war. It eventually went for around £1,150.
The 1275 went for about £700 I think, again with no ancillaries.
So I went for plan C - the other MG engine which was complete with all ancillaries (inc an HIF44), metro driveshafts and 4 pot brakes. Asking price was £1,100 and there were 20 or so people watching the item but no offers so I rang the bloke, asked if he would sell the engine without the Metro brakes etc, and got what I wanted for £850. Although not cheap, it certainly feels better value than either of the other two, especially the one that went to £1,150.
It's all a long way away from the last time I bought a 1275. It was a proper old-school scrapyard in Norwich, 1993, and there were 3 Metros sat on the grass. Two were standard and one was an MG. £40 for the standard ones or £60 for the MG. I told the bloke I'd take the MG one and would be back tomorrow with my tools to take it out. Turned up the next day and he had sold it as he thought I wouldn't be coming back. Reluctantly bought one of the standard ones instead, got a brand new 266 cam for £40 and had a great engine for less than £100!