Steve we need more information - isn't always the way!

How is your workshop fed power?
Is it from one 'way' on your house 'consumer unit' ?
If so what is the fuse there rated at,
What size (in terms of copper cross sectional area) is the cable to the workshop
How long is it?
When this cable arrives at the workshop is it terminated in a smaller consumer unit?

I assume (dangerous!) that you have a separate lighting and power circuit - is the power a radial circuit or is it a ring main?

How are you providing an earth? Are you 'exporting' an earth from the house or do you have a ground spike at the workshop?

To keep your mains 'clean' you need to avoid heavy loads switching on and off being associated with the circuit you are concerned about. Frequently causes of electrical noise in a domestic situation are things with motors, as the motor shoves spikes onto the mains at start up. So washing machines, dish washers, fridges, freezers can all be troublesome.

Let us know a bit more about the wiring so a more informed comment can be made.