Double yellow lines across the mouth of a junction have no bearing as to whether access can be gained to a road or not, they are simply put down in respect of parking and waiting restrictions.
But....... It sounds like these lines may not comply with the traffic order that has to be put in place before any lines can be put down and even then the lines have to comply exactly with what it says in the traffic order.
So for example, the traffic order may say that the lines will commence (and this is just an example) 10 yards south of its junction of such and such a road and terminate 20 yards from the junction of whatever road.
Measurements are critical as 1 foot (even 6 inches) out and the whole order becomes invalid and illegal.
Each set of lines must have termination lines
No termination lines, parking restrictions cannot be enforced
Signs must be clearly visible at regular intervals and must be at a height that would be capable of being seen by a reasonable person and the signs must comply with the lines which in turn must comply with the traffic order.
And so it goes on and I am sure you get my drift.
The point is that a high percentage of parking restrictions do not comply, and some areas are particularly bad. When I used to do traffic management, we found that something like 80% of restrictions in my area were non compliant and it still happens today as we no longer have Police traffic management checking on the legality.
You can usually obtain a copy of the order via your local library and in some areas the traffic order id also available to view online.
Might be worth having a look if you are concerned or interested.