Travelling with two pports; dual citizenship not yet official?

I recently acquired British Citizenship; previously I had a Ugandan pport with indefinite leave to remain. Uganda requires me to apply for dual citizenship but I have not done so yet. I want to travel to Uganda using my British pport on exit from UK, using my Ugandan pport on entry to Uganda; using my Ugandan pport on exit from Uganda and using my British pport on re-entry to UK. My worry is whether the indefinite leave stamp is still valid in my Ugandan passport to allow me to come to UK given my status in UK is not indefinite leave but rather naturalised citizenship. Do I need to get the certificate of dual citizenship before I travel.