Exhaust emission light came on a couple of days ago, had new plugs fitted 4 days ago. is this likely to be a coincidence as i've seen someone say it could be that the engine is not running efficiently i.e to rich/lean or are there other likely reasons can it still be driven without causing major damage

Yes can be driven with out any worries. Did the same oem plugs go in ? You can have one or more o2's that need to be replaced they dont last forever and should be treated like sparkplugs as a item to be replaced at a certain mileage your service manual might tell you when bmw suggest it. you can put it on a scanner with live data and check the operation of them they each shoul be swicthing above and below 500 rich to lean lean to rich. also live data is a easy way to look at mass air and other sensors . you can also check the cat easy way is use a temp gun check to see with the engine warmed up if there is over a 100 degree diff between in and out. you can have it hooked up to a gas ana and they can check hc co this will tell a good mechanic alot.