Hmmmmm
Unless you are totally new here, you should know by now that most of what you have 'heard' is total b*****ks! The most cursory amount of searching on this forum will give you all the answers you need, but to summarize the basics :
You can forget about getting any help with work permits from prospective employers - BALPA keep a pretty close eye on any airline trying to sneak foreigners through the system. You should be alright if you have at least one parent or grandparent born in the UK, otherwise all the relevant gen on UK work permits can be found on any of the British High Commission websites.
There is no 'shortage of pilots in the UK' as such, just highly qualified and experienced ones. There are just as many battling away on the bottom rungs of the ladder here, as there are anywhere else.
You can expect to re-sit all the ATPL theory, followed by a CPL and an IR skill test. I couldn't tell you what you have to have to get an exemption, I can tell you that I have met pissed-off Aussies with 7 or 8,000 hours metro time sitting the ATPL writtens out at Gatwick. I think you can dodge the single-engine CPL flight test if you have over 500 hours multi crew, but you'll be doing the IR test no matter what. Total cost anywhere between 4 and 10 thousand pounds, depending on where you choose to fly, whether you do a course for the ATPL writtens or just wing them, and how long it takes you to get your head around the overcrowded shambles that is UK airspace.
Even for the highly experienced, it's not a cake walk by any means - the ATPL writtens are complex to the point of sheer ridiculousness and I could name several people who've had multiple thousands of hours turboprop time from down under, who have needed a lot of dualling up and several attempts to pass the IR.
Having said all that, you'll probably find there's no difficulty getting a job - around 1000-1500 total time, or twin time in any significant amount, seems to get you into the RHS of most of the turboprops, I'm not really up with the play on jet requirements but there is loads of expansion going on particularly in the low-cost sector, and if you've got any decent turbine time I'm sure you'll be fine.
Despite the hostility, wailing and gnashing of teeth that goes on on PPRuNe every time this topic is discussed, you'll find most pilots and British people in general to be pretty friendly to Antipodeans, and there's a lot of fun to be had.
Best of luck.
- Luke ST