it'll be all right on the night

It'll be all right on the night! {UK} — не волнуйтесь, всё будет как надо; все пройдет гладко; все пройдет как по маслу (этим. театр.)

Used to say that something will be successful, even though there have been lots of problems

Some would argue that, through common usage, 'alright' (in one word) is becoming more acceptable than 'all right'. The makers of TV show "It'll be alright on the night" are known to have considered "It'll be all right on the night", but opted for the former as a more modern version.