Wow. It's taken me some time but here is the solution...
Thanks to Jim Rae for the 'wrapper class' suggestion.: https://developer.salesforce.com/forums/?id=906F000000096tcIAA.
I had to extend this to include a further level.
So, I have a wrapper that holds the Manufacturer and a list of a second wrapper.
The second wrapper holds an associated Retailer plus a list of his licences.
Here comes the code.
I've left all the debugging statements in. Also, the VF page isn't formatted. That's next...
Hope this helps a few (including anyone looking at https://developer.salesforce.com/forums/ForumsMain?id=906F000000098fZIAQ).

Enjoy.

The wrapper controller:

public with sharing class WrapperRetOfCON {
/*
This class 'wraps' data from multiple objects into one class for display in a vf page
with thanks to JimRae
https://developer.salesforce.com/forums/?id=906F000000096tcIAA
https://...visual.force.com/apex/vwWrapperRetailerLicences

'Retailers_of' records a manufacturer and the name of a retailer that sells that manufacturer's products
The retailer may have 'licences'.

*/

    private List<Account> tempAcct = new List<Account>();
    //Map holds manufacturer ID and list of their retailers
    private Map<ID,List<Retailer_Of__c>> AcctRetofMap = new Map<ID,List<Retailer_Of__c>>();
    //ManuAcctIDs is a set of manufacturer account ids used while getting retailers
    private Set<ID> ManuAcctIDs = new Set<ID>();
    
    //Map holds retailer ID and list of their licences
    private Map<ID,List<Licence__c>> AcctLicencesMap = new Map<ID,List<Licence__c>>();
    private List<Account> tempRetAcct = new List<Account>();
    private Set<ID> RetAcctIDs = new Set<ID>(); //for sub sub
    public List<wrapper> wrapout {get; set;}//the output to vf page
    
    //constructor
    public wrapperRetOfCON(){
       wrapout = new List<wrapper>();
    }//wrapperRetOfCON
       
    //wrapper 1
    class wrapper{
        
        //private variables used to set up sub-sub-level wrapper
        private List<Account> tempAcct = new List<Account>();//will hold retailer list
        public Account acctManu {get; set;}
        //This is a list of other wrappers that are nested in the top wrapper
        public List<wrapper2> retofs {get; set;}
        public wrapper(){
            if(acctManu==null){acctManu = new Account();}//initialize the account holder
            if(retofs==null){retofs = new List<wrapper2>();}//initialize the retailer wrapper listholder
        }
    }//wrapper
    
    //wrapper 2 - the sub-wrapper
    //gather list of retailers for a manufacturer
    class wrapper2{
        public Retailer_Of__c retof {get; set;}
        public List<licence__c> retsLicences {get; set;}
        public wrapper2(){
            if(retof==null){retof = new Retailer_Of__c();}//initialize the Retailer_Of__c holder
            //if(retofManu==null){retofManu = new List<Account>();}//initialize the manufacturer/Account holder
            system.debug('retsLicences= '+retsLicences);
            if(retsLicences==null){retsLicences = new List<licence__c>();}//initialise sub sub wrapper
            system.debug('now retsLicences= '+retsLicences);
        } //constructor wrapper2
    }//wrapper2
    
    //This is called by the "Run Report" Button on our VF page
    public PageReference buildwrapper() {
             
        //this will have to be expanded into a loop if # is greater than limit
        //first get a list of retailers that are mentioned in retailer_of
        tempRetAcct = [select id,name from Account where id in (select retailer__c from Retailer_Of__c) ];//limit 50
        system.debug('Retailers: '+tempRetAcct);        
        for(Account a:tempRetAcct){RetAcctIDs.add(a.id);}
        //find their licences
        
        for(Licence__c licence:[select id,name,company__c,company__r.name,active__c,maintenance_expires__c from Licence__c where company__c=:RetAcctIDs]){
            system.debug('seeking licences of '+RetAcctIDs);
            //if licence, put in Map
            
            if(AcctLicencesMap.containsKey(licence.company__c)){
                system.debug('add to '+licence.company__r.name);
                AcctLicencesMap.get(licence.company__c).add(licence);//adds Retailer_Of__c for this account to the retof list in the map    
            }else{
                system.debug('new list for '+licence.company__r.name);
                AcctLicencesMap.put(licence.company__c,new List<Licence__c>{licence});//adds new Licence__c list for this account to the map    
            }
        }//AcctLicencesMap loop
        
        
        //first get a list of maufacturers that are mentioned in retailer_of
        tempAcct = [select id,name from Account where id in (select manufacturer__c from Retailer_Of__c) ];//limit 10
        system.debug('manufacturers: '+tempAcct);
        
        //hold ids in a set
        for(Account a:tempAcct){ManuAcctIDs.add(a.id);}
        
        //then find the retailers that sell their products
        for(Retailer_Of__c seller:[select id,manufacturer__c,retailer__c,retailer__r.name,manufacturer__r.name from Retailer_Of__c where manufacturer__c=:ManuAcctIDs]){
            system.debug('seeking sellers of '+ManuAcctIDs);
            //if seller, put in Map
            if(AcctRetofMap.containsKey(seller.manufacturer__c)){
                system.debug('add to '+seller.manufacturer__r.name);
                AcctRetofMap.get(seller.manufacturer__c).add(seller);//adds Retailer_Of__c for this account to the retof list in the map    
            }else{
                system.debug('new list for '+seller.manufacturer__r.name);
                AcctRetofMap.put(seller.manufacturer__c,new List<Retailer_Of__c>{seller});//adds new Retailer_Of__c list for this account to the map    
            }
        }
        system.debug(AcctRetofMap);
        
        
        
        
        
        //now put results into wrapper for display on VF page
        for(Account aa:tempAcct){
            //create and fill a new wrapper object then add to wrapout
            wrapper tmpwrapper = new wrapper();
            system.debug('transferring '+aa);
            tmpwrapper.acctManu=aa;
            list<wrapper2> t2 = new list<wrapper2>();
            for(Retailer_Of__c oo:AcctRetofMap.get(aa.id)){
                wrapper2 twrap2 = new wrapper2();
                system.debug('oo='+oo.retailer__r.name);
                twrap2.retof = oo;
                twrap2.retsLicences=null;
                //make a wrapper list of licences
                list<Licence__c> templic = AcctLicencesMap.get(oo.retailer__c);
                if (templic != null){
                    list<licence__c> t3 = new list<licence__c>();
                    for(Licence__c ol:templic){
                        system.debug(ol.name+' ret='+ol.company__r.name);
                        t3.add(ol);
                        
                    }//ol
                    twrap2.retsLicences=t3;
                    
                }//templic
                
                t2.add(twrap2);
            }//oo
            tmpwrapper.retofs=t2; 
            wrapout.add(tmpwrapper);//that's a manufacturer and it's retailers plus their licences add to the output object
        }//aa

system.debug('Wrapout: '+wrapout);
        return null;
    }

    
}