"The promises he has made before have related to things like restricting which days he drinks, what he drinks, and keeping note of how much drink he can take before getting 'too drunk'.
He has stuck to these".
No he has not because he breaks any self imposed boundary he cares to set. This coming from a man who drunk a bottle of vodka a day in his 20s. My guess also is that he is still badly underestimating how much he is drinking.
"He only drinks on a Friday and/or Saturday. He only drinks Fosters as spirits, cider and other beers seem to effect him badly. He has cut down to 4 cans over the last year. He used to drink between 4 and 8, but it made the over drinking more likely".
You make that sound like a good thing. It truly is not
"We was trying hard to stick to the 4 can and no more rule (and that's usually all that he buys) - but although he does fine 90% of the time he has these laspes where he'll come home with more and just plough through them".
Not "we". It needs to be him and him alone. You must stop trying to police and or control his drinking; that way madness lies.
So he will drink tonight then. If he is an alcoholic he should not be drinking at all.
I would read the following below because this relates directly to you. You seem to be at stage 2 now, you have a long way to go:-
Stage 0: Does not recognize or admit that there is a problem. Often denies it outright. Enables alcoholic’s behaviour.
Stage 1: Admits that there may be a problem but does not admit the degree to which it affects them. Often blames themselves for the alcoholic’s drinking, especially when the alcoholic gets angry. Fixes problems caused by their alcoholic’s drinking. Sometimes gets angry with their alcoholic. Continues to enable alcoholic’s behaviour.
Stage 2: Truly accepts there is a problem. Starts to confront or challenge the alcoholic’s drinking. Tries to control the alcoholic’s drinking. Makes bargains with them to cut back on their drinking. Often gets angry with their alcoholic. Often without realizing it, they are still enabling the alcoholic’s drinking behaviour.
Stage 3: Realizes that they do not know how to control the alcoholic’s drinking. Looks for outside help, generally not for themselves but for their alcoholic. Anger can increase along with sadness and depression. Still enables alcoholic’s drinking.
Stage 4: Realizes that, regardless what their alcoholic does, they need help to deal with their own life problems. Begins looking for help for themselves; has not yet stopped trying to control the alcoholic. Starts to find out about options for dealing with the problem. Still enabling their alcoholic. Still expresses anger, sadness and depression.
Stage 5: Accepts that there is nothing they can do about their alcoholic’s drinking behaviour; that all they can deal with is the things over which they have control. Begins to learn about acceptance and detachment. Begins to recognize and quit their enabling behaviour. Gets involved in a group therapy program. Works on personal and spiritual development. Works on improving financial situation.
Stage 6: In recovery. Reconnects with family and healthy friends. Gets involved in new interests that are not drinking related. Makes new friends. Improved financial situation. General contentment with their life in spite of their alcoholic’s behaviour.