If you have mild kidney disease, going on holiday shouldn’t pose additional health problems, whether you're staying in the UK or going abroad.
The following sites offer general holiday advice:
The NHS will look after you if you get ill while on holiday in the UK. If you’re travelling you can apply for healthcare cover abroad (GHIC and EHIC). For most people, the UK Global Health Insurance Card (UK GHIC) replaces the existing European Health Insurance Card (EHIC) for new applications. It entitles you to free or reduced-cost hospital treatment subject to the specific country terms. For those entitled to continued cover under the EHIC scheme you can find more information about it here: EHIC - European Health Insurance Card - SchengenVisaInfo.com
It’s a good idea to take out holiday travel insurance in addition to carrying the GHIC/EHIC. Anyone with kidney disease should declare it as a pre-existing medical condition on standard insurance application forms. It may exclude you from some policies.