Craig, who was also known as Stuta, helped care for his grandmother at the South Lanarkshire Council-owned property.
After she left the house to move into Rodgerpark Nursing Home the council changed the locks and the family were unable to get in to obtain the suit and other personal items, such as Craig’s birth certificate.
Kathleen said she pleaded with the council for keys to the flat.
However, Craig had to be buried in his favourite white McKenzie t-shirt and blue and white Gio-Gio tracksuit bottoms.
The 50-year-old mum added: “They wouldn’t let me in to my mum’s house so I could get my son’s suit for his funeral and that really upset me.
“I felt really bad but we buried him in his good tracksuit.
“These are the things that really hurt me.
“Before my mum went into the nursing home, Craig and I had cared for her, but the council changed the locks.
“There are lots of photographs of Craig stored there as well that I can’t get my hands on.
“It’s hard enough that every time I step out of this flat I have to look at where it happened.
“Could they not have had a little bit of compassion?”
A spokesman for the council said: “We were contacted for access to the flat at Chapel Court, Rutherglen, (for the purpose of obtaining) documentation relating to the late Craig Thomson.
“However, we were unable to provide access to this tenanted property without being given the appropriate consent to do so.
“Unfortunately we were not made aware of a request for other items required by the family.
“Otherwise it may have been possible, with the appropriate authority, to have facilitated this.”