Trip back to the UK in May

[cannondale]

We are travelling to the UK for three weeks from the end of May to see family and go to a wedding in Dublin.

As we are flying into London Heathrow, we need to hire a car for three weeks and return to the same place.

Does anyone have any recommendations for which company to use or who not to use for that matter? Appreciate we will probably not be allowed to take the car into Ireland for insurance reasons.

Also, does anyone have any recommendations for a pay as you go sim card for data and calls to New Zealand from the UK?