Dear KellyP,
I noticed in your first post that you said you were both upstairs when your dog went to the toilet downstairs - sometimes, their signs are subtle, and you may have missed a certain restlesness ... If in doubt - take out !!
Everyone expects the odd accident (even into adulthood, if we are careless) but I guess that living in a bungalow means that for a good deal of the year I can leave a door or patio door open so my two can go out when they need to. Now that it is wet and manky, however, I have to reinforce the 'tiddly-widdly' and 'quick'quick' routines so that when I let them out in the morning, at lunchtime etc. they actually do their jobs ! Jeremy is home mid-afternoon, so there are not many accidents, but we do sometimes get woken at 4am by someone who 'forgot' to go at 11.30!
DO reinforce the widdle routine and get them used to going last thing - otherwise, contain them in a place where there is some paper or an easily cleaneable flooring so no-one gets stressed if an accident happens !