The implication here is that, say, a family of two adults and two kids would pay £58.70 + £58.70 + £29.35 (child fare version of same ticket) + £29.35 = £176.10.
But, that's an 'any permitted route' and peak travel ticket.
Not necessary for Clapham-Bletchley which has a direct train so no need to go via London. If peak travel is necessary, then the cost changes to £150.90.
If peak travel isn't necessary (ie can wait until after 9am) then an adult ticket becomes £26.50 and a child ticket £13.25 giving a total of £79.50.
But then a groupsave fare automatically applies to three of those tickets meaning the total becomes £65.60.
A family without a car would very likely invest in a family & friends railcard - giving a 1/3 discount on the adult fares, and a flat fare of £10 for each child, meaning the total cost for a family of 4 is £44.90. That's a return ticket - as long as you depart after 9am.
So by travelling off peak and choosing the right ticket, the total cost for a family of four is about 2/3 the price of the ticket for one person that you've shown.
And this is why I argue against the simplistic notion that the UK has the "most expensive fares in Europe". Yes, peak travel is expensive, but very often off-peak travel really isn't, and there are further discounts available to those travelling in groups who might otherwise be able to share a car.