What do I need to do to fix a Vauxhall Zafira 2ltr Engine management light?

Zafira on an 03 plate - 2.0ltr Dsl.

1. Orange Engine managemant light can be on at start from cold or hot and goes off after 10 mins. It can be off at start and come on when running but dosent affect the running.

2. When driving car running normally no engine management light (orange) on - when increasing power to go up hill or when increasing power to overtake Orange engine managent light comes on and loss of power felt in engine (no smoke from exhaust) and engine goes to limp home mode. If you pull in and turn off the engine the fault clears and engine is back to normal however, the fault re-occurs intermitantly. This can happen after 10 mins of driving or after 2 hours.

3. Any advice woud be much appricated as I have to go from the south coast to Glasgow shortly.