The group behind strike-hit Southern Railway has insisted it is improving performance for long-suffering passengers, but warned over an ongoing blow to rail profits after annual results fell.

David Brown, chief executive of transport giant Go-Ahead, told the Press Association the group had cut cancellations by 75% and boosted train capacity by 36% on some Southern lines despite ongoing industrial action.

He said he could not offer long-suffering passengers "guarantees" of an end to strikes, but was "resolute on trying to improve performance on Southern and put all this behind us".

Go-Ahead - which runs Southern through its Govia Thameslink Railway (GTR) joint venture with French firm Keolis - posted a 5.7% drop in pre-tax profits to £136.8 million for the year to July 1.

Rail earnings tumbled by 16% to £59.9 million, with the ongoing industrial action and service woes on Southern seeing GTR suffer a 3.9% drop in passenger journeys and a 4.1% drop in revenues.

Shares in the group fell 6% as it also warned rail profits would remain under pressure in the new financial year after losing the London Midland rail contract, as well as a drop in passengers at Southeastern amid a wider slowdown in the economy.

Mr Brown said the past year had seen "challenging market and trading conditions" in its rail and bus businesses.

He said: "We apologise to our Southern passengers who have been inconvenienced for many months by disruption caused by industrial relations issues.

"Service levels are beginning to improve but there is still a lot of work to be done to provide the level of service we and our customers expect."

Southern was ordered to pay for a £13.4 million package of improvements by the Government in July, which will see it fund 50 non-board supervisors and other projects to boost service levels.

The firm has been in a bitter row with unions over proposals for so-called driver-only operated trains, but GTR has also admitted it underestimated the impact of extensive railway improvement works.

The Southern dispute started more than 16 months ago, and the Rail, Maritime and Transport (RMT) union has taken 34 days of strike action, while there have also been six days of walkouts by the drivers' union, Aslef.

Mr Brown said the company's switch to driver-controlled trains meant the most recent RMT strikes had a "minimal" impact on service.

But the group admitted the industrial action over the past year had caused "significant disruption" to the network.

It said the penalty imposed by the Government had helped resolve "financial uncertainty" in the division, although it remains in talks with the Department for Transport over contract changes, which could still affect annual rail profits by up to another £5 million.

The full-year figures showed bus earnings were also under pressure in the year to July, down 0.5% at £90.7 million, dragged lower by the regional bus business.

Go-Ahead is now targeting growth abroad, with aims to make 15% to 20% of profit overseas within five years as it faces challenges in its domestic market.