I made some little rubber feet to fit on the bottom of the rear legs of the seat.  Sure as the D***ens, the seat back releases and the seat rocks forward for access to the rear seats.  You learn something everyday.

I was thinking that as the Mk1 Minis had no latch (my memory served me right!), the original design of the Cobra seat did not provide one either. Maybe they have not bothered to update the design. My mid-'80s Mini does have a latch system.

No, the original MkI seats were not anchored at the rear.  But Kolsen’s original post said he was having problems with his “aftermarket Cobra seats”.

Obviously you need adaptors to fit these to a Mini... and part of adaption needed (IMH is to bolt the back legs to the floor.  I use small spreader plates above and below the floor.

In later years (mid 70s) the authorities (in Oz) did require rear latches so Leyland welded small tabs to the rear outer legs of each seat and these locked into matching spring loaded tabs welded to the floor.

Cheers, Ian

Mine certainly doesn't and don't see any place either on seat or floor for same.  Think there is just supposed to be a little wear strip in the carpet for the rear legs to rest on (need to chase that down).  Seat belt cinches everything/everyone down. 
Kim 
Morris 850 MkI

It wasn’t in Parnell book

Makes me wonder: did original MK1 Mini seats have the hold-down latches?

Well I guess that's the way it was manufactured.  When I pulled the seat there was no provision to attach the rear to the floor.  I never considered the requirement to rotate the seat forward to enter the rear.  So even though I tried to attach the rear to the floor, I ended up putting the seats back in like they came out.  Lesson learnt

If yours is like mine (IMH the base is too short and the rear legs end up too far forward.  They seem to sit around my centre of mass leaving a lot (well... not that much perhaps ) weight hanging over the back.  The square base is also bolted together (30 year old generic Cobra base for Mini) with no cross bracing so has no diagonal integrity...

You can (I have) bolt the rear legs through the floor (haven't had anyone in the back in 20 years).  I'm about to implement what I think will be a better solution by extending the base so I will be sitting within the four legs rather than on top of the rear two.

Cheer, Ian

Or bolt it to the floor and zoom around like a 914 ??

Check the front seat brackets where they bolt to the floor.

Hard to say for sure what you are dealing with without photos. Maybe there are only two bolts holding the seat to the seat base? Typically the seats are not fastened to the floor at the rear. They need to pivot up for access to the rear seat.

Went for a drive with some other British car owners.  Out to the coast at the mouth of the Columbia River and then down the Oregon coast.  Felt my seat was a little loose.  Got home and lo and behold the after market Cobra seats where never attached to the floor at the rear, just resting on the floor.  Well that will be fixed tomorrow.