I require a chaperon, and am glad to find one.

I will join your party, paying my own hotel and travelling expenses, and considering myself as engaged in case your wife should need my services.

For that, you can pay me, if you like, some nominal retaining fee--five pounds or anything.

The money is immaterial to me.

I like to be useful, and I sympathise with nerves; but it may make your wife feel she is really keeping a hold over me if we put the arrangement on a business basis.