The first time he saw it was in 2005 when an American collector contacted him to verify whether the letter -- estimated to be worth 7,000 pounds ($11,000) -- was genuine.
It was 25 years after Lennon had been shot dead.
"It was so frustrating because Lennon even included his home phone number on the top of the letter," said the 60-year-old. "I know it's silly but I wanted to ring him up across the ages."
Tilston added he "felt rather angry to start with to think that someone had just sold the letter rather than passing it on to me, but you have to let these things go."
Lennon wrote to Tilston: "Being rich doesn't change your experience in the way you think.
"The only difference, basically, is that you don't have to worry about money -- food -- roof etc.
"But all other experiences -- emotions -- relationships -- are the same as anybodies, I know, I've been rich and poor, so has Yoko (rich -- poor -- rich) so whadya think of that.
"Love John and Yoko."
Despite not receiving Lennon's reassuring words, Tilston still went on to record more than 20 albums and will mark his 40-year career with a special concert next month.