Nah. Not saying there isn't any truth in what you surmise might be their "plan" more that planning isn't this governments strong point.Unless as pointed out above this was an accidentally on purpose plan.
Let as many non vulnerable catch it as possible but retain plausible deniability that this was the intention by saying it was really naughty newspapers who printed the story of a plan they were trying to keep from them until Monday
So its their fault really not the government.
And/or the naughty people who went crazy all weekend expecting it be off the table next weekend - so breaking the rules by default. When, of course, they should have known better.
Someone else to blame either way as no government can knowingly encourage young people to go out and catch it as some will inevitably get ill. Though they calculate not many will be very ill. So on balance may be good.
If secretly that's exactly what they would like them to do but for obvious reasons could never say so. As encouraging people to get sick is not going to win many votes.
May not be what is happening. It could just be incompetence. There is plenty of precedent for that. But it would be stupendously incompetent to keep on giving weekends notice to let the virus spread one last time before publicly claiming they now have to do all they can to stop it spreading.
I think it more likely that it is perceived or actual pressure from the industries involved. In other words, money.