Travel chaos is expected in London as thousands of bus workers began a 24-hour strike over pay.

Around 5,000 bus drivers walked out at 3am from two London bus firms, First and Metroline.

Unite has called the strike in support of a campaign for a single pay rate of £30,000 a year for a 38-hour week for drivers, arguing that pay in the capital's 18 bus companies varies by up to £6,000.

Unite officer Peter Kavanagh said: "There is a startling disparity between bus drivers' pay in the capital, with rosters in some companies seeing many drivers complete nearly 60 hours a week.

"Not only is this potentially unsafe, it is unfair to have bus workers across London doing the same job for less money or having to put in longer hours."

The dispute is set to escalate, with Unite balloting workers in other bus companies for industrial action later this month.

Adrian Jones, managing director of First bus company London & Berkshire, said: "The union is intent on dragging further bus companies into strikes in pursuit of its fruitless bid to standardise conditions of working and pay in all companies.

"Transport for London deal with each contracted operator separately and have given no indication that they would be willing to change the way in which routes are bid for to allow for a single pay structure.

"First's bus drivers are already amongst the best paid bus workers in London. Between 2003 and 2007, First's bus drivers' pay increased by 34 per cent, during which time inflation has increased by only 16 per cent. Most drivers receive over £25,000 a year and this rises to over £30,000 a year for a normal rostered week for over a quarter of drivers."

The disruption will not be as serious as it could have been after another company due to be affected won a legal challenge to stop their staff walking out.

Metrobus said its services in London will be running as normal after it successfully lodged a legal challenge against Unite.

Unite said it was "astonished" at the court decision as it had held previous strikes at the firm and believed it had fulfilled all the "strict" legal obligations covering industrial action ballots.

From 0300 Friday 10 October, until Saturday morning, the following routes may be withdrawn or severely reduced:

4 6 7 10 16 17 18 23 28 31 32 43 46 52 58 67 70 79 82 83 84 90 91 92 95 98 105 107 113 134 139 140 143 150 165 179 182 186 187 189 191 193 204 205 206 207 210 212 214 215 217 223 224 226 232 234 236 240 245 251 252 259 260 263 266 271 274 282 295 297 299 302 308 309 316 323 326 328 331 332 339 341 357 365 383 384 385 389 390 399 414 427 460 476 487 488 603 605 606 607 611 616 626 632 640 643 646 649 650 652 656 679 686 692 699 953 958 A10 C2 C11 D6 D7 D8 E1 E3 E5 E6 E7 E9 E10 H12 PR2 RV1 U1 U2 U3 U4 U5 U10 W5 W6 W7 W8 W9 W10 W11 W12 and ELW.

Heritage service on 9. School service on 370. Night services N5 N7 N10 N16 N18 N20 N28 N31 N52 N91 N98 and N207. The Metroline garage at Brentford is not involved in this action, so a full service operates on Routes 117 190 209 237 609 635 E2 and E8.