The episode numbering on this series has always been a bit odd.
The Channel 5 info is incomplete, but https://www.channel5.com/show/traffic-cops/
indicates that we are currently on Season 7. Note; ignore anything listed for 5Spike, it just runs repeats.
Unfortunately the more compete information at Radio Times https://www.radiotimes.com/tv-programme ... ode-guide/
says that we are currently on Season 5.
The TVDB seasons (6 & 7) are currently aligned to the Season listed by Channel 5 (the transmission network)
The requested Seasons (4 & 5) are those of Radio Times (the "authoritative" UK TV liking guide).
I cannot check EPG info; the current episode has no Season or Episode information and I have no recorded episodes that I can check.
On the whole, I feel that TVDB is right in following the Season number of the TV Network... unless anybody has a better argument.