Yeah but see Gavroche's post #12. Actually cars are only allowed to pass objects that are stationary or travelling at less than 10mph in a double white line system. It's another case of the letter of the law vs the spirit. Assuming your speed is <10mph, a car driver who overtook you with plenty of room but crossed the double white line would be committing an offence. The same car sneaking past you with half an inch to spare would be within the law (double white line rule), though he would also be in contravention of the rule that says he should pass you with "as much space as you would a car". Seeing as one rule is fairly nebulous and ill-defined, but the other states clearly that you must not cross or straddle the DWL, most cagers would go for option 1 rather than wait.
129
Double white lines where the line nearest you is solid. This means you MUST NOT cross or straddle it unless it is safe and you need to enter adjoining premises or a side road. You may cross the line if necessary, provided the road is clear, to pass a stationary vehicle, or overtake a pedal cycle, horse or road maintenance vehicle, if they are travelling at 10 mph (16 km/h) or less.
163
… give motorcyclists, cyclists and horse riders at least as much room as you would when overtaking a car (see Rules 211-215)