If you are working, that is being paid, then you need to comply with the law with respect to electrical safety, not just the installation work your undertaking.
Under the MHSAW and the HSAW employers and employees have a legal duty to undertake risk assessments for all work they undertake and to reduce the risks to the lowest economic/practicable level. The work you will be doing means that other acts come into play, such as PUWER, CDM and related regulations depending pon what your doing and what equipment your using, such as scaffolding, MEWPS etc.
Now under the CDM regulations and the guidance given out by the HSE for the use of power tools in work environments, bear in mind although it is a home, you are actually working and thus fall under the general scope of the regulations involved, the HSE state the following..
HSE Guidance said:
Tools, plugs and cables designed for DIY and domestic use are not suitable for site conditions. You should use cordless tools or those that operate from a 110V centre tapped to earth (CTE) supply system so that the maximum voltage to earth does not exceed 55V.
Regularly inspect power tools and take them out of service if they are damaged. Tools should be serviced by qualified electricians. Do not do makeshift repairs.
Clearly although it does not ban the use of 240V tools it does strongly suggest you should not, and generally with the HSE that means you do so at your peril because it it goes wrong and they can demonstrate you have not taken reasonable care , ignored the regulations and guidance or otherwise worked in a dangerous or reckless manner they can and do prosecute.
I would hope regardless of your position on the use of 240V tools though, if you do that they have an RCD attached to the lead at some point for added safety.