Mr Red,
I'm sure you in the UK.
Dog Borstal is good for tips, on BBC3, new series just started on Friday eves.

Following on from Liz, above, after feeding take said canine for walk on lead and reinforce the need to pee and poo with whatever words you want but be consistent, no good me saying "do a wee/do a poo" when you say "banana/apple" for the same commands/responses.
While the dog does its business keep repeating the words, and reward after.
It will soon associate its actions with your words and do it on command.
The only other option I can see is an indoor kennel/cage and keep the dog in it when you are out, as they will almost certainly not soil their own space.

Geoff (owner of 15 month old Polly, Black Labrador who can go for days without peeing and then pee every 2 mins when out - lol)
www.webfolk.net
Don't allow it to wander off and do its business away from the lead, that way you help it to do it with you and for you.
NEVER punish the dog for getting it wrong.