Bought new bike at weekend and man in lbs put saddle to right (?) height. It feels a touch high to me feel like I couldn't put feet anywhere near floor if I needed to - yes I know brakes are the main stopping mechanism. I thought it was a case of one foot on pedal and the other should be able to touch floor relatively easily is that not the case. Now to be fair the major test took me unintentionally though some very muddy woods and the mongoose 450 isn't designed for that and I frequently found myself having to dismount (well practically falling off - was longing for my giant back at that moment) - I went out with no map and followed my nose! Unfortunately I couldn't adjust the height when out as the back light fitting was in the way - had the tools but went without glasses so couldn't see to do the job!
So what is the view on saddle heights please.
So what is the view on saddle heights please.

Yeah it does sound like that doesn't it however it is perfectly natural to do. You just stand up on the pedals and you will high over the saddle, move your posterior forward and you will now be over the top tube where you can now safely put your foot on the ground without any problem. The bike frame may be just a little big for you if you have can't stand flat footed on the ground and have a inch clearance over the top tube however you should still be okay because when you come down off the bike to put your foot down you will naturally lean the bike sideways in the direction that you are putting your foot down and that will give you a bit more clearance anyway.
That's the way to go. To be honest the council run the schools so why they couldn't have thought of that themselves is a bit worrying but good on you for sorting it.