Nothing to do with 'Lou Grant' this time....
It's a given that TV characters in the main Toobworld have doppelgangers in the alternate TV dimensions, including The Tooniverse and the sketch comedy world.
Here are some examples as proof of that:
Lennie and Squiggy ('Laverne & Shirley') and Vinnie Barbarino ('Welcome Back, Kotter') - 'Saturday Night Live' 10/15/94
'Lou Grant' - 'Saturday Night Live' 11/17/84
The cast of 'Murphy Brown' - 'Family Guy' 4/18/00
And then there are times when Toobworld is bypassed completely as happened with the Coneheads. The aliens "from France" were from 'Saturday Night Live' and they also got their own cartoon pilot aired. (And then they have Cineverse counterparts as well.)
Usually, the TV characters originate in the main Toobworld and then go off to the sketch comedy world. But that's not the case with Andy and Lou of 'Little Britain', who are two of the creations of Matt Lucas and David Walliams, respectively.
Lou is a kind-hearted guy in Herby City looking after the needs of Andy who is disabled and in a wheelchair, and is probably mentally challenged as well.
At least, that's what Lou believes. In actuality, Andy has been taking advantage of Lou's kindness by faking all of his problems. When he wants to, Andy is perfectly capable of stealing police cars, riding horses, and carrying on deep philosophical conversations.
So now it looks as if Andy and Lou have their counterparts in the main Toobworld, because they'll be showing up in the Australian prime-time soap 'Neighbours' sometime in May. (Williams and Lucas have already filmed the scene.)
In their scene, Andy and Lou are in Erinsborough, the fictional contribution to the geography of Toobworld. At the Scarlet Bar, they'll be interacting with regular characters Steph and Toadie.
I've never seen the show, so I can't vouch for these characters as being a big deal in terms of with whom Andy and Lou could have appeared.
These versions of Andy and Lou should be considered different from those to be normally found in 'Little Britain'. (If anything can be considered normal in that show.) If taken as a whole, 'Little Britain' has a different Prime Minister than Tony Blair, who at present is the PM for Toobworld and the Trueniverse. Prime Minister Michael is in charge at Number 10 Downing Street for 'Little Britain'.
The crossover cameo on 'Neighbours' will be affixed to the Toobworld timeline as having occurred in May of 2007, since that is when it will be first broadcast. But viewers in the UK will have to wait until later in the year before they can see it. (Unless it shows up on bit torrent, I think 'Little Britain' fans in America are right out of luck.)