As the streams of fans moved towards the Brandenburg Gate to watch Germany's World Cup matches, few noticed the men and women standing with bags and carts by the entrance to the fenced-off arena, collecting empty bottles.

Nadine, a pregnant 20-year-old, had been stationed at the west entrance near the Victory Column since midday, and her shopping trolley was half full. Empty glass and plastic bottles can be redeemed at German supermarkets for eight to 25 cents (6-20p) an item. "Twenty euros should be in it for me today," she said.

Asked why she was collecting bottles, Nadine replied: "There are private reasons. But let's just say, I wouldn't be doing it if I didn't have to."

In recent months, these Pfandsammler (deposit collectors) have become increasingly controversial, with some cities accused of trying to push them out of their centres.

Hamburg now has 160 solar-powered bins that squash rubbish, allowing them to be emptied less frequently. Stuttgart has installed bins that store waste underground. The effect in both cases is the same: collectors can no longer reach inside for bottles.

Stephan Karrenbauer, a social worker, said the move in Hamburg was part of a deliberate strategy to cleanse the city centre of unwanted social elements, something the council denies.

"If you don't have any money in Hamburg, you've got three options: you can go begging, sell Hinz & Kunzt [Hamburg's equivalent of the Big Issue] or start collecting bottles. So if you block up the bins, you are pushing a lot of people into abject poverty," he said.

In response to the public criticism, the city has since installed "bottle shelves" on some of its bins, allowing passersby to leave empties for the collectors, and similar designs are being tested elsewhere.

A spokesperson for the Hamburg's public cleaning services claimed that the shelves had been a great success – though critics question whether six holders per bin are likely to make a difference.

In Berlin, where one in seven citizens lives on the verge of poverty and there is no ban on drinking alcohol on public transport, bottle collectors have been a social phenomenon since the 2006 World Cup. Yet this year most of the big public screenings do not allow people to bring their own drinks, and bottle collectors are often barred by security staff.

"You can forget it this time," said one man collecting bottles outside the Brandenburg Gate. "In the past, you could earn a fortune."

But Germany's Pfandsammler resonate on a wider political level. Hard-working, orderly and environmentally friendly, workers in the bottle-recycling sub-economy embody some of the more positive values associated with Germany.

Some argue, however, that they stand for a new social class whose existence the government is trying to deny: people with irregular incomes or who are on basic state benefits, who need top-ups to survive in what is nominally Europe's richest economy. Many are pensioners.

"Politicians don't even recognise this group – they just ignore them," said Sebastian Moser, a researcher at the Max Weber Institute in Lyon, who last year wrote a doctoral thesis on the Pfandsammler phenomenon. As an exception, he mentioned the leftwing Die Linke party, which ran a poster campaign during last year's election that read: "Instead of collecting bottles: €1,050 minimum monthly pension!"

The controversy in Hamburg, Moser said, was indicative of the state's growing neglect of people whose lives were precarious. Citizens were left to compensate for the public sector's retreat. He talked of a privately run website called pfandgeben.de, which puts collectors in touch with people who want to get rid of bottles they have amassed at their home or office.

From an ecological perspective, Germany's bottle deposit scheme – implemented in 2003 in the face of opposition from manufacturers – is generally seen as a success. A 2010 environmental agency report said the scheme "leads to less rubbish on our streets and squares". But it made no mention of the informal economy that has grown around it.

After spending two-and-a-half years interviewing collectors in several cities, Moser concluded that money was rarely their sole motive. "For many, it is an attempt to escape from loneliness. Finding bottles and returning them gives people the kind of recognition they no longer get from their job or family. If the state wants to help, it should think about how it can integrate those whose social support system has collapsed."

As the Berlin crowds cheered on their team, a pensioner ambled away with a bin bag full of bottles on her back. "In the past, my husband and I used to go collecting together, but since he's died I've had to carry them by myself," she said. "I'm alone now, but when you're out and about collecting bottles, you get chatting with people."