I believe this to have originated from chavs/townies/mods of today. From what i have observed and practiced this word usually replaces a >doing word< such as "pass" or "come" etc. This may be a regional thing but it does save alot of effort even if you are not a chav.
Some unfortunate people are unable to grasp this concept and just use the word "llow" in the wrong place as shown below.
"llow me that ruler"
"where do you wish to go today?"
"let's llow the town"
"argh! some idiot llowed me this f**king cold!"
"have you got the llow?"
(this time llow could mean a thousand things)
"llow me the time, please"
When you think of something that you need to do but you really cant be bothered to do it. The lazyness of humankind catches up with you and you really just give up and go to sleep.
Person A "Gotta do my homework today man..."
Person B "llow it"
Person A "Alright, lets play Halo"