What are the regulations for having glasses during landing?

I always thought that glasses had to be collected and my experience has always been that the crew pro actively offer plastic cups. However, on my recent flights this was not the case. LHR-GLA I held my glass in full view expecting the crew to offer me plastic and take it away. I was ignored. On the return GLA-LCY the crew member told me to keep the napkin in case I spilt my drink on landing! Is this a breach of procedure or has something changed?