I suffer from blocked ears during landing from time to time as well. Have discovered Menthol Crystals recently. It works wonders for me whenever I have blocked ears or feel them coming on. I use them just before starting decent, together with swallowing hard and gently blowing my nose if necessary. It has never failed to unblock my ears or even prevent me from having it. You might have heard of them, they are like Karvol but much much stronger. The first sniff you take is like whooa, strong stuff!!!
You can buy them in Boots, behind the counter. Hope it helps.
I also think that Boots own make Decongestant and Nasonex nose spary is great stuff, but the latter is prescribtion only...