Hi RickyR,
Firstly, congratulations on Marvie`s successful visit visa application.
I have been to UK on Visitor Visa and I did not have any problem at all entering the UK.
When I present my passport to the Immigration Officer,
"what`s the purpose of your visit?" that was the question asked.
Thats all.
Although I heard and seen on TV program that some people have a hard time entering the border even they have a valid visa, I think that is when the Officer found someone looks suspicious.