'It looked like a stage set for the First World War. This was once excellent farmland and the houses were beautiful. Some of the heaviest fighting took place in this sector. Now it is all damaged,' he says.
And yet on meeting Help the Aged's workers, who have been running two programmes since last summer - home visits and counselling for the elderly - he was cheered by their enthusiasm: 'I am impressed by their sustained energy,' he says.
Help the Aged is making home visits to about 1,600 elderly and vulnerable people still living in their own bomb-damaged homes, or those who are displaced and living in shacks, or sharing homes. They also visit those living in larger barrack-like camps, on both sides of the moveable border in Sector West. One home visit can take up to about four hours, depending on the needs of the older people, many of whom are in their eighties.
'Some are terribly frail and need food, medicine and fuel brought to them. They need time-consuming assistance regularly and this is very wearing for the workers. But others are fiercely independent and proud,' explains Mr Mayo.
At Okucani, Mr Mayo visited 19 older people squashed into a partly converted house. Nine women share one room, and 10 old men share another, their beds crammed in tightly with barely six inches of space between each one.
'It is basic. They sit all day in their rooms. There is no bathroom and the lavatories are bad. What we need to do is build a bathroom which would cost about pounds 5,000 to really transform their lives,' says Mr Mayo. As he talked to the older people he saw their sadness immediately. 'They looked helpless and hopeless. It doesn't take long to bring tears to their eyes. The misery on their faces is shocking. In the past, when I was a soldier, I worked with refugees in Europe but they were nothing like this'.
Members of the 80-strong visiting team, which includes a doctor, two physiotherapists, two social workers and 15 nurses, can be dealing with extreme shock and certain embarrassing dilemmas. Sometimes the younger helpers find themselves helping people who they knew before the war. Previously, they had a happy family life and would never have needed help, but now they have lost everything.
Help the Aged is pleased that its home-visits scheme has been imitated by the UN and other helping organisations. 'It isn't earth-shattering, I know, but it is good, solid, plodding rehabilitation work,' maintains Mr Mayo.
The charity's other programme, based in Verazdin and Zagreb, is counselling the elderly who are suffering from post-traumatic stress. 22 refugees and displaced people have been selected for training so that the work can be extended. 'The training has given them back a little self-respect, they have started to pay attention to their appearance and have visibly brightened up,' says Mr Mayo.
The deepest pain for so many people, displaced or not, is loss and shock. While in Zagreb, Mr Mayo met a displaced Bosnian couple, aged 65 and 68 - although they look much older - living in a bitterly cold tin shack with two rooms. Before the war, he was a civil engineer, they owned a smallholding with cows, chickens, fruit, vegetables, two cars and a comfortable house.
'They made a success of their lives, brought up their children well and now their whole life has been destroyed and they can do damn all about it, drifting along at someone else's whim. It is absolutely humiliating, it is terribly cruel and it is not their fault,' says Mr Mayo.
To continue both its programmes at the present level for a further year after this March, Help the Aged will need to raise a further pounds 200,000. More will be needed if the charity expands its programme to other regions.
The Independent Bosnia Appeal has so far raised pounds 234,583.95. The money has been sent in by readers to help 15 charitable organisations working to ease the plight of the 2.7 million people in former Yugoslavia who are entirely dependent on aid. For every donation to one or more of charity, the Independent will add 10 per cent, up to pounds 30,000. The appeal closes on 31 January.
If you would like to support it, please send a separate cheque for each donation, made payable to the organisation - with the wording as below - and send to: Bosnia Appeal, The Independent, 40 City Road, London EC1Y 2DB.
1 War Child; 2 Victims of War Appeal (former Yugoslavia) - this for the Red Cross; 3 Care; 4 Cafod (Bosnia); 5 Christian Aid (Bosnia); 6 Edinburgh Direct Aid; 7 Feed the Children; 8 Help the Aged Former Yugoslavia Appeal; 9 Islamic Relief Bosnia Fund; 10 Marie Stopes International (Bosnia); 11 Oxfam; 12 The Refugee Council; 13 Save the Children Fund; 14 Scottish European Aid; 15 UNA Trust Bosnia.