It doesn't say in the BA ops manual you can land on a runway with an aircraft blocking it. It also doesn't say you can't. pilots are selected and trained to use common sense and judgement to maximise safety and efficiency.
All things being equal if the revised LDA at ACC was greater than the ED at the alternate, provide consideration was given to GA profile then it seems ok to me.
Before I landed I'd consider the problem for the crew getting the jet out of there however.
A friend of mine used a very similar example to this demonstrating his attitude to risk at an interview for a major carrier recently. He passed.