Possible Clues:

• I'm opposed to a railway with no concrete base
• Illusory
• Not based in fact
• Like some friends or numbers
• I'm getting old, short and fairly regularly ignored -- it's not real!
• It's all in the head of one famous mother downing a ruinous drink
• Not real
• The setter's ace trap -- a set of lines that's not real
• Pretend one woman's astride another
• One contrary girl swallowing a drink? It's not true