Just 50 people. That's how many foreign workers PricewaterhouseCoopers, which employs 18,000 UK staff, will be allowed to bring into Britain this year. And the accountancy firm is not happy.

PwC is not alone. Across the UK, banks, law firms, carmakers and industrial companies have been agitating vigorously about the coalition's draconian crackdown on the immigration of highly skilled staff.

This week, they thought they glimpsed a chink of light. The home secretary, Theresa May, announced on Friday that certain international transfers of existing employees within companies will be excluded from quotas placed on the number of overseas hires for big businesses. But the Observer has learned that this exemption on "intra-company" visas is likely to be tightly limited. Tentative proposals floated by ministers would allow firms to transfer overseas staff earning over £40,000 into the UK. But entry for lower paid workers, particularly those on less than £24,000, is set to be severely restricted.

May's concession came hot on the heels of another quiet shift – a refinement of visa renewals that allows companies to extend the stay of foreign workers already in Britain. That alleviated fears that big firms would have to start sending London-based international staff back home within months.

Company-by-company limits placed on foreign recruitment in July have been a source of intense anxiety. Many of the City's top banks, which have huge multinational workforces, were capped at around 40 foreign hires. One major drugs company was given an allowance of fewer than 10 visas.

The caps are part of an effort to achieve a Conservative manifesto pledge to reduce immigration from hundreds of thousands to "tens of thousands" annually. Businesses complain that they are being targeted because it is easier to address legitimate migration than illicit entry.

Japanese carmakers, including Honda, Toyota and Nissan, were only given a handful of permits but insist that they need to be able to bring technical experts from Tokyo to work at British factories. "Intra-company transfers are essential for our business to operate," says a Nissan spokesman. "They're clearly not the type of migration that the government was hoping to target. They're very small in number but essential for us."

In the Square Mile, senior sources say that disquiet over caps was sufficient for some banks to threaten a rethink over investment in London. An executive at one bank says that a block on transfers within companies could put "a serious check" on growth: "That new investment wouldn't be coming to London if you don't have the visas to slot people in to expand the business and grow by bringing in that person who, say, runs Turkish operations."

Many investment banking firms headquarter their entire European and Middle Eastern operations from London and argue that they need people with a knowledge of markets in many different nations. They complain that the Home Office devised the bespoke company-by-company limits by taking firms' visa applications in 2009 – a low point for recruitment because of the recession – and then imposing arbitrary cuts of 5% to 15%.

Julia Onslow-Cole, head of global immigration at PwC, says her firm needs "significantly more" visas than its cap of 50 simply to renew expiring permits of workers already in London. She welcomes the refined criteria exempting renewals from the immigration cap: "The government announcements on the interim quota regime, guaranteeing extension applications, and the exemption for intra-company transfers in the final cap will be very welcome not just for PwC but also for our clients."

But in spite of last week's concessions, businesses still have major concerns. The Commons home affairs select committee recently recommended that international transfers within companies should be limited to two-year assignments, and immigration minister Damian Green has suggested visas will only be made available to people above a certain level in seniority, pay and skill. The government is to set out its full policy by the end of the year, with revised caps for companies to be introduced in April.

But the Corporation of London, the local authority for the Square Mile, was heartened by the pledges made on Friday. "The City welcomes the general direction of travel… We are also grateful that the home secretary acknowledged legitimate business concerns about the proposals," says a spokesman.