More great advice and ideas, thanks.
Tango sounds very much like Maddie, I really dont think he'd care if I went home while he is exploring.
Agree about the use of "this way" rather than "come, or here", it does seem to get a bit more of a reaction.
Not sure if it was the correct thing to do but went out on a longish (about 15ft) lead today and tried the treats thrown around me - it did keep his attention but I dont really know how much of that was really just down to the lead stopping him running off. I also stopped occasionally en route and did some sit, stay, watch commands to vary things. Then reached one of the more open wooded areas where we normally play ball and as he had been pretty good up til then I made the mistake of unclipping the lead but, after just two throws, you guessed it...... straight off into the undergrowth with the ball still in his mouth. To be fair, I just stood still and kept quiet and he came back (sans ball) to check within a couple of minutes - before going off again once he saw me - but I had him back on the lead after a few more minutes and so to home. I have to say he looked pretty fed up when we got back and has been subdued all day, so I guess he's probably quite confused!
Clearly got an awful lot of work to do and bad habits to correct (me and tango).