Part 1 (Masters, Experts and Novices)

Start at the southernmost roundabout in GS8233.
Proceed via the following roundabouts entering at the first colour and exiting at the last (NTRs are included).

YYYY   WYW   WWWW   WW   WYY   YYYY   WYY   YYYY   YYW   WYY   YYYY   YYY   YYRRYRRRR
RRWWRR   RRRRYYY   WWWW   WWWW   YYYYY   WWWW   YYOOOO   OOOORRRR   RRWWRR
RRYYYRR   RRYYRR   RRYYRR   RRGGGGR   YWWYW   WWW   GGGGYYY. Finish at GL88.

Part 2 (Masters Only)

Continue via:

1  7  1.25  0.5  0.25  1  2  0  1  1  5  1  2  0  1  1  0.5  2.5  2  0  3.75  11.25  0  1 1  0  1  0 .75
0.25  0.75  4  0  0  1  0. Finish at T.

Hint: The number of roundabouts in a ?

Oh, you do not like roundabouts. The lowest ranked Route Card.

With the notoriety of Milton Keynes roundabouts it seemed like a good idea at the time to base a Route Card on them. Maybe the density of detail for such an urban map was just too much for your eyes.
The infamous concrete cows were featured too - plural. So "Cows" were passed not "Cow" (rule 24).
It wasn't definitive which was the last (T)elephone - so 8934 or 9034 were correct.
The sequence 1 0 .75 should have (more precisely) been 1 0 0.75 - but you sussed it.

"This one drove me a little crazy." Shane Glynn
"I shall be counting roundabouts in my sleep now!" Nigel Parish

Route Card Winner: Iain Tullie