Hi!
There's no legal requirement that I know of to state that you are in a proposal, if you are not asked about it. If asked if you have been insolvent or sought an insolvency solution, the answer would be of course be yes. But if they don't ask, I would assume they are not worried about it! You are already their customer, so they know your payment habits with them are good. I agree with Wetcoaster above - if it were me, I would just take the offer.
~Wendy