..... but I have been compliant with US tax requirements for the past few years (I filed tax returns and FBARs for 2010-2012). I have also had returns and FBARs prepared for me for 2008 and 2009 but not filed these as they were late.
Well done, you are approaching this in a very rational manner. If you have already filed for 2010, 11, and 12, and will file a return for 2013, you will have 4 years. You will have to file for 2013 (and FBAR), no way out of it given the circumstances.
As I am going to renounce, I would like to do so as cheaply and easily as I can which is why I am wondering if I could file my 2008 and 2009 forms now and be able to tick the box saying that I have complied despite these being late..... Just to be clear on the filing on the 8854, if I were to renounce this year, I would have to file a return for 2013 this year and then the 8854 next year?
If you renounce in 2014, I believe you will have to file a return for 2014, even if it's a part year return. That would give you 5 years ('10, '11, '12, '13, and 2014).
If you wanted to be safe, you could file '09 by a 'quiet' disclosure (just send it in now). Supposedly, FBARs (both past and present) must now be done over the internet with the Treasury Dept. There are risks associated with doing this for both the tax return and the FBAR, and you need to research those. IMHO, there would be no need to consider the 'streamlined' disclosure route since you have already filed for the past 3 years. Others may disagree.
If you renounce in 2014, then yes, you would file the 8854 in 2015. The 8854 not only checks you out of the system, but also gives your position regards the exit tax, if applicable.
Being as you have already filed the returns for 2010-12, and have the return for '09 prepared, it makes sense (after the expenses) to renounce. I assume you are aware there is a $450 additional fee to be paid for renouncing (at present).
There are those on this site that are going through renunciation at present. I would hope they may comment, giving a more accurate perspective.