First question here, thanks in advance for any responses.

Basically, I have lost pressure from all the hot water taps/shower in my house.

Boiler seems to be working okay - water is actually hot but initially comes out as usual for half a second when turning taps on, but then slows to a trickle.

Everything was fine last Thursday when I had a shower before going to work, but has failed to work properly since.

Any suggestions?

If every single faucet has reduced pressure for hot only go back to your water heater/bolier. Check the pressure coming out of the boiler. It is probably partially plugged with scale.

Disassemble the outlet to the water heater and check for full flow. Is a valve partially closed?