Need to renovate property, but want to keep good tenants (SE13)

Possession - Section 8 and Section 21

2 bed town house in Lewisham, London SE13.

The house has not had a single void day since 1997, current tenants (one of whom shared with the original 1997 tenants) have been there since 2005. Never paid a day late or a dollar short.

The house has been kept in good decorative order and clean by the current tenants. I only get callouts for major items. The property is long overdue for renovation as kitchen and gas boiler are from the early 1990's, and the bathroom and the house electrics are from 1960!  

The electics failed the EICR and the gas boiler is on it's last legs, I'm just hoping it will make it through the winter.

Renovation will take about 3 months and cost well over £30k. The house will not be habitable during the renovation. There are zero short term/seasonal rentals in the area and AirB&B start at £4k PCM

I'm going to have to more than double the existing rent once the property is finished, but is there any way I can keep my existing tenants (or at least give them first refusal ) or do I simply serve a section 21 notice to Quit and just leave them to sort out a new home ?