Airline A to back and forth to NY.
Airline B NY to MCO. So two airlines two separate bookings.

So problem occurs if flight A from UK is late and I miss the internal flight to MCO. Even worse, return B is late and I miss the transatlantic back to UK.

Bearing in mind this is likely to be a cheap ticket, not a flex as well.

Done indirect in the past albeit with same airline. In scenario 1 they just put us on later internal flight - inconvenient but hey ho. In scenario 2, they paid for a hotel overnight and we went home next day.

In all likelihood what would happen:-

1. UK to NY is late so we miss connection to MCO.
Is it likely airline will try and put us on later flight FOC or will it be tough buy another ticket?

2. MCO to NY is late so we miss UK. This could be worse - with just one flight a day its possible next days might be full too.

Of course, one solution is to fly to NY stay over one night then fly to MCO. Same coming home. Even then its not foolproof.

Not even sure if travel insurance would cover a missed connection like this? I know it covers missed departure (e.g. car breaks down on way to airport, public transport failure etc) but not sure about halfway through your trip like this.