2001 Renault Megane Burning Oil

Smells problem
2001 Renault Megane Front Wheel Drive Manual 106350 miles

Hi - have just had my car MOT'd and it passed - even emissions! There is blue smoke coming out of the exhaust and I did ask the garage to take a look. Could not find anything wrong but agreed there was smoke. Using about 1/4 litre every 100 miles. Performance is fine - acceleration is as good as always for a 1.9i - no loss of water. Is it OK to drive a car like this topping up with oil when needed - will I do any damage? Would an additive help? Need advice please as I would have thought, if there was a problem, the garage would have fixed it - they can't afford to turn work away. This is also a garage I have used for the last 8 years and they are brilliant! Any advice would be gratefully received - I love my car and don't want to get rid of it! Thanks