Can you build a conservatory OVER a drain access ( leaving some sort of access inside ) or do you need to move the drain access ?

No but you will need to replace the lid and frame with a sealed one, they have a rubber gasket and screw down.
i would'nt advise covering it and forgetting it though, some folks do and when the drain blocks you have to dig the floor up to get access.

thanks for quick reply 40summat. very useful

Check that the manhole is just for your property too, if it is a shared drain and your neighbours are running through it there is a much bigger chance of a future blockage and all the problems with them needing access that occur.

Can you build a conservatory OVER a drain access ( leaving some sort of access inside ) or do you need to move the drain access ?
Not wanting to state the obviuos , but you will need access. be careful what floor finsh you put down. If you put down a floating floor on batterns over the drain then it will be less visible. But you will have to lift the entire floor to get access. Carpet would be you best bet over boards. When laying the boards make sure you mark out the drain so that you know where it is at a later date.

Also, although you will not need planning for the conservatory, you will have to inform the local authority if you plan on cover the access point up.

.. although you will not need planning for the conservatory, ...
That isn't necessarily true