Done this trip earlier this year although I didn’t overnight in London. On arrival into NBO you will be taken by bus to arrival terminal 1E. On departure it will be the main terminal you will use and it’s usually Gate 14 for departure.

The lounge that is used is the current TK lounge which is very basic. Food isn’t great and the lounge tends to get quite full. There are no toilets in the lounge never mind a shower. There is an Aspire lounge right next door but not sure if that has shower facilities or if BA passengers can use it.

As kosy91 says, the KQ lounges have showers however, don’t think you can pay to get in to use them and they looked pretty dismal when I was there a few weeks ago.

Have your vaccination certificates ready for when you get off the bus as these will be checked before you are allowed into the terminal. You should also attempt to register on the PanaBios website. I was asked for the trusted traveller certificate too when I last arrived (6 weeks ago) and I think you have to still complete the MOH online for, which gives you a QR code that they sometimes check.

Safe travels. I’ll be passing through NBO on my way home for a break in a couple of weeks time, unfortunately having to pass through terminal 2 which is nothing more than a very big tent.