Settlement fees where valid cca in place

The biggest question is are the debts still with the original creditors or with a debt collection company.
Debt collectors pay a much reduced amount to buy out a debt (despite what some on here say the banks rarely loose out as they will usually have had payments above the original principle, plus the amount from the debt collectors and the rest they write off against tax). This amount is typically around 20p in the £1 but can be as low a 2-3p in the £1.
The general advice is to start low with offers, say 10% of the balance and negotiate hard with the company. If you have already being making payments, you may have already covered the fee the debt company paid so they will be even more open to offers.
If the debt is with the original debtor they may be less amenable to low offers, but made decide a bird in the hand is worth 2 in the bush so to speak. Otherwise make out a SOA to send to them and stick to your guns. Don't let them push you into a payment plan you will struggle to meet. Better to have a plan you can stick to and save any extra to clear debts off early.

When making full and final offers ensure the offer is accepted in writing (never over the phone as they will frequently lie about what was agreed and you have no proof unless you have the means to record the calls yourself-you muct inform them before recording).
Ensure they accept the offer in "full and final settlement" and to confirm that there will be no attempt to collect the left over balance by themselves or any other third party.

You could also ask for other conditions such as default removal or at least a guarantee the debt will be noted on your credit file as "settled in full, with a zero balance" rather then "partial settlement", after all it is a negotiation so you want the best deal you can get. But that is up to you.

Ensure all agreements are confirmed in writing by them, and keep this document at least 6 years (if it were me forever lol).

Some of the debt charities have templete letters for negotiating full and finals, as do a number of forums.

Good luck

ali x

PS Having reread you original post it may that the debt hasn't gone as far as a debt collector, when you talk about "sending the boys in" remember anyone who isn't a baliffs ie any debt collector who tries to call has no more powers than the avon lady and less than a postie so you can tell em where to get off. As long as you give them your full situation they should continue to accept your payments if that is all you can afford. At worst they may insist that the account is defaulted (if it hasn't already) and pass it to their in house collectors who will then agree a payment plan with you.
Remember if it went as far as court (unlikely if you are making offers and sticking to the plans agreed) the judge will force them to accept an amount you can afford, takling into account all your bills and other debts.

As you sound like you are still in the early stages it may well be worth contacting one of the debt charities to help you negotiate payment plans.