Crank and bottom brackets are fairly straight forward to remove if you have the correct tools. For £40 you should be able to buy the proper bb removal/installation tool and a crank arm puller with money left over. Study Park Tools' web site for step-by-step directions and the recommended tools. I assume Park Tools are available to you or there are other good makes.

You probably should let the shop remove the headset cups (and the crown race if you're having the fork done) and reinstall them when the job is complete.

What make and model crank and bb do you have? It would be easier to recommend a substitute if we knew where we are starting.