Nope, would not want that for my kids.
In primary we already try to squeeze all the maths and literacy into the morning lessons because that's when the children are at their brightest, and that is when they learn. We try to keep the afternoons for sports, craft, IT, nature studies - less intense lessons.
In case anyone out there is thinking that perhaps it would be a great idea to stick an extra maths lesson for this age group in at, say 3.30 ... you are seriously deluded! NOTHING would get learned. By that time of day the average kid is lolling in their chair, has an attention span of about 5 mins. and needs to be allowed to stitch off, with a change of scenery and pace. ie: home or a relaxed after school club.
I'm also mulling over the ways in which the government would manage to wriggle out of paying support staff for these extra hours while the classroom are all still in use. TAs etc already tend to do at least 30/45 mins unpaid work per day. In the empty classroom at the beginning and end of the school day, doing displays, sorting equipment for the next day, helping lesson plan with the teacher, sorting lost property, printing off letters, printing off work sheets etc etc etc. These seem like small considerations - but if the school is still in full swing and full of pupils at 4.30/5pm, when is all this going to get done? Later and later. (and will these staff ever get paid for it?)