I reckon it's OK to pass, as long as you match your passing speed sensibly to a respectable bit faster than the speed of the cortege..... for example:
When my Nan died, she was living near us (Reading) but her wish was to be cremated and ashes interred down in Worthing where her family home was and where Grandad was too. So she was prepared and readied by our local firm and then driven down in the hearse on the morning to Worthing Crem for the funeral. We (Mum, Dad, Sis and I) had to arrive before she did because she was going to be borne into the chapel by her 4 sons, so my dad needed to be there for a crash course in pallbearing with his 3 brothers.
Unfortunately, traffic around Dorking was awful and both we and the hearse were held up badly. In true family tradition, we'd been late in setting off so we were wellying it down the A24 with no hearse in sight. We finally passed her doing 95 just north of Washington about 2 miles shy of the crem, with about 3 mins to the appointed hour.
And we were pissing ourselves laughing, because the local undertaker was Tony, my best mate from school's dad, who had a look of steely determination and a fixed gaze as he piloted this hearse down the A24 at speeds far from those considered 'respectable' in the trade. And secondly - because Nan was a reknowned back seat driver, and even in death we could all imagine her banging on the lid and berating him to slow down.
Being an ex-publican, it was a hell of a wake too!