Do I need to inform the dvla of a auto to manual swap?

Same here, I said I would be very happy if they took the auto bit off the model but they refused.

Road tax was abolished back in the 30's IIRC.

its an E30 318i, so no it wont affect the Taxation class.

I informed DVLA a few years back about a auto to manual conversion with pretty much the same results as the other posters. They just weren't interested at all.

On a slightly separate note but related to DVLA & their ways.
My last kitcar was registered correctly (pre sva) but the model type was recorded slightly wrongly (2x2 instead of 2+2).
Several letters and phone calls got it changed to something that was still incorrect (2xx2) that led to more letters and eventually they changed it back to what it originally was.
I gave up eventually and had to put up with the inevitable questions at insurance renewal time why a 2+2 was registered as a 2x2.

I had similar with a RWD Nissan 200 many years ago, the engine was good but the autobox died so I converted the car to a manual.
DVLA weren't interested but my insurers wanted an engineers report as the vehicle was now "heavily modified"
- my argument was that it was the same car & engine, with a different factory box but they didn't see it that way (I changed insurers before I insured it...)

Insurers are so strange, mine are the opposite of yours, because mine has the correct 5 speed box that the car would have come with from the factory as standard as a manual, they are totally fine with it.

Contrary to all of the above, just before Christmas I sent off a v5 with a covering letter asking for the auto part to be removed from the model designation.

Whether it was down to the (true) statement that it was needed off as we'd done a manual conversion and the new owner needed the v5 to be correct for importing into another country, I don't know, but they obliged without drama. Either way,they did do it, and sent it back to our UK address, without being asked to prove the export.

It can do when the RFL is determined on emissions. Certain Saabs for example are around £200 dearer to tax for the autos as it bumps them up into the next emissions band.

its a 1987 E30, no.

Simple, it's not done with the car static.

While the car may not be 'moving', the wheels are turning a dynamometer and this is programmed with the rolling resistance of the car - simulating a moving vehicle including all the forces on it at a range of speeds.