I've bought liquid Persil Top Loader Sensitive - let's give that a shot!  Was tempted to buy their "high performance" one - but what additional chemicals it might have, who knows?
I washed the washing machine physically using a pot scrub and a bottle brush to get inside the agitator (it had some sort of schunge in there 
).  I washed and rinsed all the removable parts.  Then I put through a hot empty wash.  When filled with hot water I put in some vinegar (about half a bottle) and a good handful of baking soda.  Not working off any recipe here but knew there was enough baking soda/vinegar when the water starting fizzing slightly.  
Would be interested in home made washing powder recipes - I'm going to Bin Inn tomorrow.