ok, I hope you've done a search on the CAA's website and worked out what you have to do.
LASORS That'll spell out just what you need. Note the rules about training in one place and flying in another. I have also posted at length about the conversion process.
At the moment because you don't have 500 hours multi crew time then you won't get a JAR ATPL. Instructor time is fine but nothing spectacular here. There's enough instructors here competing for the next step up. To get the attention of the Brits you'd want to have some turbine time, preferably jet time. (yes, I know what you are thinking...)
There's several things you can do. Firstly, get the Australian ATPL finished. To minimise your exposure to financial drama, I would do your theory part time/distance learning through Bristol Ground School. Note, you'll have to come over here to do the exams.
Medical, do at Gatwick.
Theory, do at Bristol Ground School.
Flying, I'm afraid I can't strictly advise. You'll need to do a min of 15 hours to convert the IR. THere are some other Aussies that have done the flying here. Look at PAT at Bristol, I think Tayside has a good rep too (In Scotland).
How long will it take? It depends on how you do the theory and if there's any resits etc. Allow a potentional 6-12 months.
Budget at least $35,000. You have to consider the MCC as well plus living expenses.
If you are coming here on a UK Grandparent visa then you are restricted to living in the UK untill you have a British passport.
I am sorry to sound a bit negative about your instructing time however, it's still a tough market for non turbine people here. If you can, get some charter time in Oz. Why? You just might find that Oz is easier and cheaper. Yes, the market is slowly changing here and should get better 2004-2005.
PS the Aussie licences are valid for life, the UK/JAR licences are not and must be renewed. Therefore, get the Aus ATPL.