Broker Tullett Prebon said trading activity had slowed in recent weeks, leaving its revenue for the year flat on last year, after a stronger trading period to the end of last month. Tullett said in an emailed statement on Friday that revenue for the four months to the end of October was 8 percent higher than last year at 315 million pounds.

But the broker added: Market activity slowed towards the end of the period, and revenue in the month of October was 3 percent lower than in October 2010. The trend seen in October has continued into November.

Tullett said its year-to-date revenue to the end of last month was 769 million pounds, flat on the same time last year.

A research note from Numis said: We forecast £900m of revenue for the year down 0.9 pct and see no reason to change our forecast as we assume November and December will be similarly weak as October which was down 3 pct.

The Tullett statement came two days after Tullett's main British rival ICAP said its revenue for the six months to the end of September was also flat on last year at 867 million pounds, while profit inched up 2 percent to 186 million.

We are living through extraordinary times in financial markets. Global imbalances and slowing economic activity are being played out together with the Euro zone crisis, ICAP chief executive Michael Spencer said on Wednesday.

The climate of uncertainty is inevitably creating risk aversion in volatile markets around the world, he added.

Tullett, ICAP and rivals BGC Partners and GFI Group , which match the buyers and sellers of bonds and swaps, are hopeful regulatory changes in the United States and Europe will boost their business.

Lawmakers are keen to force large swathes of the vast $600 trillion over-the-counter (OTC) markets to use regulated platforms and the brokers are developing their systems in the hope of being the vendor of choice when the laws take effect.

Tullett said on Friday: We believe their introduction will be positive for our business as the proposals formalise the role of the intermediary in the OTC markets.

ICAP's Spencer said on Wednesday he was frustrated by the slow pace of regulatory reform but remained positive about the effect of the Dodd-Frank rule in the U.S. and the Mifid II and Mifir market reforms acts in Europe.

Tullett said: The detailed technical rules will be finalised by the European Securities and Markets Authority, and it is envisaged that Mifir and Mifid II will come into force during 2014.

(Editing by Jon Loades-Carter and Will Waterman)