Just to show that even those of us who've had the T25 for a few years now can also make elementary mistakes ....
Having done ~1,000 miles over 10 days to the Bashtie and back I was accelerating away from a roundabout near my Mother's house and the engine suddenly revved higher seemingly on it's own

the the oil buzzer (of doom) came on

So I stopped
immediately so as not do any further damage and opened up the back to have a butchers. Everything seemed in order ... no glaring oil leaks, no drips, nothing

So I checked the oil, which when you've just switched off the engine is elsewhere than on the dipstick. Feeling uncertain I added some more oil and set off (gingerly) for home.
As the engine revved above 2,000 rpm the buzzer came on again but the engine was running absolutely fine ... no rattly empty tappets, no knocks or bangs ... just the kin B.O.D. Drove carefully through Bakewell and out home the scenenic route (i.e. NOT through Matlock at 5pm

) After driving up a long hill there was suddenly a cloud of smoke behind the van so I stopped immediately and called ADAC to recover me home.
This morning I (and a chum) pressure checked the pots (all were 105 to 110 psi) so we dropped the engine oil ... expecting loads of metal

... however as I went under to drop the oil I noticed the brown wire was off the B.O.D. sender and there was a nick in the (quite slack) 'fan' belt

and there was 5 litres of oil (plus 1/2 in the filter) instead of 4 litres

Replaced the B.O.D. wire, replaced 4 litres of oil, replaced fan belt, fired up, no smoke, no buzzer just as it should be.
Just to show that we can ALL make mistakes and 4 (VERY experienced) owners on here, who I asked said they would have done exactly the same thing as I did. That buzzer was working perfectly but it creates panic even in the old and gnarled amongst us. Hope this helps others
Ian.