Bay Laurel Tree - leaves turning brown

puddy

I have 2 small bays that we bought last summer in big pots outside the front door. its sort of sheltered and receives more or less full sun as its south facing. Im not sure really when it started but the leaves have started turning brown, but only on the tips and it moves down to cover the whole leaf. I have searched the internet and some pictures show browning but only around the edges. it also states that brown leaves affected by this and that, fall off, my leaves havent fallen off they have stayed on the plant and last weekend when taking them off, they were quite stubborn to remove. there are some green shoots coming through, im hoping they dont go the same way.

the plant was out in the snow we had in winter but i cant detect any mites or lice or anything. some of the leaves were webbed together with white stuff but not many