Harry ji, I understand how it is to not be able to read and understand punjabi text.
It's never too late to learn, believe me.
I am like you, born and raised british with all things english. Infact, I was one of the very few that was already a generation ahead in the 70's as my father was even born there in UK back in 50.
I have somehow managed to learn how to read punjabi. This has all been self taught although as a youngster I did go to punjabi school but as you know none of us really learnt anything useful in those times.
It's still tough at times, but I keep trying.
I actually learnt a lot of my gurmukhi from Japji sahib!!!
You see, at first I would listen to it repeatedly, listen,listen and listen. When listening, I actually paid a great deal of attention to the words and pronunciation. Then eventually, I became very familiar with it, say in about a year.
Then I started to read it from the gutka and it became alot easier, as I would be familiar with a lot of words. All this helped me learn to read punjabi and gurmukhi. With only knowledge of simple alphabet and kiddie vocab!!!
I am still learniing, and enjoy doing the sukhmuni sahib translations line for line and word for word. I do still get a blank when I see huge pieces of text to read in punjabi but it is best done word for word.
If you keep at it, it will become easier. Practice,practice,practice...
Although I am able to read it, sometimes a little slow, I can't write it!!
I wouldn't know where to put Prakash ji's siharis and biharis when it came to it.
But, I find it''s the reading that is easier and more of what I need. I have never come across a moment where I desperately need to be able to write it.
This is just my own method of how I came to learn to read it. When I tell others, especially ones that read and write punjabi very well, they are always shocked that I have sussed the language in this backward way!!
Believe me, it's not rocket science or difficult but involves patience and time.
You do the mool mantar, I would say try memorising a couple of pauris a time. When you know them a lot better, then start trying to read them.
It does sound a little backward, because I learnt the words 1st, then applied them to the text to understand the text, BUT it has worked for the little that I do know.
I do wish though that the small punjabi school classes we had as 'fun' and 'messing about' were better taught and a little more serious. I mean nearly all the muslim kids there learn the arabic and koran from a young age. The punjabi needs to be taught with better methods.
Keep trying, don't give up, it's not as hard as you think.