That is indeed what it is.
To enlarge a little though, it was not intended to be a Jensen as such. For the Jensen design Jensen had asked Leonard Lord for an A70 chassis, which he readily agreed to provided Jensen would design them a body for a sporting car to sit on their A40 chassis, and that is what this is a prototype for. Unfortunately the design wasn't ready in time for the motor show, as you say, where Lord spotted the Healey 100 and forgot all about his Jensen-designed car......!
The design on the A70 chassis went on to become the 541/first Interceptor, but Jensen did still produce a body for Austin to mount on their A40 chassis, the A40 Sports, about 3200 of which were produced and which didn't look like the puzzle car at all. The puzzle car is also variously described as a prototype for that car.
The other car you have pictured has also previously been a puzzle on AP (one of mine actually!)