I can't see that allowing people outside to take exercise more is going to increase the risk - the problem arises from being close to someone infected or from touching a surface that has the virus on it. So being allowed to go further for walks etc, with your own household is not going to make things worse.
It might actually help - I think many people are getting so fed up with lockdown that more and more people will start breaking the rules. Maybe if they are relaxed just a little, to allow people to spend longer outside, they will be more willing to keep to the rules.
It'll be interesting to see what Wales comes up with - so far, our First Minister seems to make a point of saying the exact opposite of whatever Boris does. We get our announcement tomorrow - no doubt trying to get in ahead of England so he can prove he's not following what they say. I am getting tired of the political point scoring going on between the various countries. Having different rules for Wales & England is especially stupid - I can cross and recross the border several times on one short journey, so how Wales is going to police a stricter lockdown than England is anyone's guess - people in East Wales will simply border hop!