I don't think there is much you can do about Fridays, given the country that we have and given that you have to be in your constituency. Some people have these horrific commutes, as has been mentioned. I would hope that by having a four-day week you wouldn't turn Thursdays now into Fridays, in other words with no votes, no committees, and so on. You would have to see how that works.
If Thursday was a normal day, as it is now, and Friday was off, I don't think you would be losing that much.