Right, added the line to /etc/sysctl.conf and restarted. Still no joy getting the eth0 link up. Syslog reports:

May 25 19:56:31 khoxlx00250 kernel: [ 2716.300005] wlan0: disassociating by local choice (reason=3)
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) starting connection 'Auto eth0'
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  (eth0): device state change: 3 -> 4
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) Stage 1 of 5 (Device Prepare) scheduled...
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) Stage 1 of 5 (Device Prepare) started...
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) Stage 2 of 5 (Device Configure) scheduled...
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) Stage 1 of 5 (Device Prepare) complete.
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) Stage 2 of 5 (Device Configure) starting...
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  (eth0): device state change: 4 -> 5
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) Stage 2 of 5 (Device Configure) successful.
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) Stage 3 of 5 (IP Configure Start) scheduled.
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) Stage 2 of 5 (Device Configure) complete.
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) Stage 3 of 5 (IP Configure Start) started...
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  (eth0): device state change: 5 -> 7
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) Beginning DHCP transaction.
May 25 19:56:34 khoxlx00250 dhclient: Internet Systems Consortium DHCP Client V3.1.1
May 25 19:56:34 khoxlx00250 dhclient: Copyright 2004-2008 Internet Systems Consortium.
May 25 19:56:34 khoxlx00250 dhclient: All rights reserved.
May 25 19:56:34 khoxlx00250 dhclient: For info, please visit http://www.isc.org/sw/dhcp/
May 25 19:56:34 khoxlx00250 dhclient:
May 25 19:56:34 khoxlx00250 dhclient: wmaster0: unknown hardware address type 801
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  dhclient started with pid 3715
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  Activation (eth0) Stage 3 of 5 (IP Configure Start) complete.
May 25 19:56:34 khoxlx00250 NetworkManager: <info>  DHCP: device eth0 state changed normal exit -> preinit
May 25 19:56:34 khoxlx00250 dhclient: wmaster0: unknown hardware address type 801
May 25 19:56:34 khoxlx00250 dhclient: Listening on LPF/eth0/00:01:02:04:98:61
May 25 19:56:34 khoxlx00250 dhclient: Sending on   LPF/eth0/00:01:02:04:98:61
May 25 19:56:34 khoxlx00250 dhclient: Sending on   Socket/fallback
May 25 19:56:37 khoxlx00250 NetworkManager: <info>  (eth0): carrier now OFF (device state 7)
May 25 19:56:37 khoxlx00250 NetworkManager: <info>  (eth0): device state change: 7 -> 2
May 25 19:56:37 khoxlx00250 NetworkManager: <info>  (eth0): deactivating device (reason: 40).
May 25 19:56:37 khoxlx00250 NetworkManager: <info>  eth0: canceled DHCP transaction, dhcp client pid 3715
May 25 19:57:07 khoxlx00250 NetworkManager: <info>  (eth0): carrier now ON (device state 2)
May 25 19:57:07 khoxlx00250 NetworkManager: <info>  (eth0): device state change: 2 -> 3
May 25 19:58:07 khoxlx00250 NetworkManager: <info>  (eth0): carrier now OFF (device state 3)
May 25 19:58:07 khoxlx00250 NetworkManager: <info>  (eth0): device state change: 3 -> 2
May 25 19:58:07 khoxlx00250 NetworkManager: <info>  (eth0): deactivating device (reason: 40).