Hi Jonathan and welcome to the forum
The starting point is really working out your disposable income - I have a form on my website which you may find helfpul, and then determining how much you could afford to continue to pay your creditors on an ongoing basis. If you could post this information, we can assist you further. If you can afford £545 per month, and were just suspicous about paying it to someone you had never met, then an IVA appears to be viable, but you need more detailed advice on this from an insolvency practitioner.
Is an IVA the only option you have considered, or have you also thought about bankruptcy proceedings as well. This may be a better option for you, if you have no assets. I would not recommend a Debt Mangement Programme given the high level of your debts.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
For further details contact me at
http://www.melaniegiles.com and view my IVA blog at:
http://melaniegiles.blogs.iva.co.uk