Do I need to rewire garage or is it a fault with electricity

Sounds like your circuit wasn’t designed for the amount of power your using. Your best getting the current electrical system check by an electrician, explain what your looking to use it for and having them calculate if it’s sufficient.

There are a few reasons this could happen, most likely is that you are overloading the circuit feeding the garage causing it to trip out. You may need a bigger supply installing just to feed the garage or upgrade the garage circuit to a ring main and install a larger fuse size at the consumer unit. Without having a look at the installation and with the limited information provided this would be the likely cause and resolution.

If you have all loads on at once, it maybe an overload issue but if not It's unlikely tripping out because you are overloading the circuit and it's also unlikely you need a rewire. What's more likely, is that you have a loose connection in a socket somewhere, a damaged cable or a faulty rcd/rcbo (trip switch). It is, almost certain that you need an electrician, not only to find and rectify the fault but to make sure there are no more existing faults on the circuit and everything is safe. It's good to remember, trip switches are only applied as additional protection to an installation, second to decent earthing and should never be solely relied upon as prevention from electric shock and installation failure.

Power tools take a surge of electric on start up. This can cause the circuit to trip out. It would be best to get a competent electrician to check the wiring and advise the best course of action. I would recommend rewiring the garage and if needed updating the supply cable.

As with most things electrical. Get a registered electrician round to have a look and advise you on what's best.

Sounds like a faulty RCD or overload on the circuit