This is a new one on me -the usual practice with this particular lilac is to stop it flowering for the first couple of years by nipping off the flowers as they form to give the shrub time to establish itself properly, and I've certainly never heard of nipping out centre buds to encourage flowering.
If it hasn't flowered this year, it should next year, but perhaps its growing conditions aren't as good as it would like - as you're a guest it's impossible for you to answer questions under here, but I'd like to know how big it is, exactly how long its been planted for, and whether it's in a shady or sunny spot, and what kind of soil you have - I don't know where you are in the UK so I can't even take a guess at what kind of soil you might have, nor whether you're somewhere very cold or not.