How to terminate wires?
Will it be fairly safe to terminate the wires using screw terminal blocks like these? 


Permanently

Although UK connector blocks of that type are rated for 400V AC 30A. As far as I know, any unused wires should be either removed completely or alternatively, disconnected at both ends, and connected to ground at both ends. This is so that a circuit breaker trips immediately if the wires are ever accidentally made live. All connections must remain accessible via a cover plate, you can't just plaster over where the light fitting used to be.

One important objective is to avoid creating an invisible and illegal lethal electrical hazard for the next family that move into your home.

Temporarily

What you propose is perfectly sensible for a temporary arrangement during painting of a wall or ceiling. Temporary in the sense that normal arrangements will be restored within a day or so.

You don't need a 30A connector for a lighting circuit, a smaller 6A connector is fine for a typical UK 6A lighting circuit. This is enough to ensure that the breaker trips before the connector catches fire in the event of a mishap such as accidentally flooding the connector with conductive paint.

The purpose of the covering is to keep the liquid paint out, so it probably doesn't need to be electricians tape. That would probably be convenient though.