Regarding bus operator in UK

I would like to know why the bus operators in UK love to take all the retired buses from Hong Kong to use rather buy
the buses? What are the main attractions on all the retired HK buses in the operators' point of views?

1. Passanger service:
they are cheap, and many of the services- on which the buses are used -are not making enough money to justifying new buses.

2. sightseeing buses: the buses offer more seats upstairs than the normally shorter UK buses. but new engine emission standards in Europe might change all of that...

3. School buses
The buses can take at least 80 people. buses in the UK take less, so certain school routes can accomodate the larger buses ,and, therefore you need less school buses. it saves money. in addition, outside London ,school buses are tendered for old buses to save money.
many school buses only run to and from school and do not work any regular routes [but may work at weekends on rail replacement services]

4. rail replacement buses
again, the buses are cheap, they are larger than the average UK bus, and they are not always used extensively.
it is a tradition to keep old buses for rail replacement duties.

in short, the ex HK buses are old therefore cheap, and can accomodate more passangers. this can be used in certain commercial situations in the UK.

regards

Yoram