I’m in New York on holiday (got out of LHR yesterday!) so this won’t be the most detailed of posts.
De-icing of aircraft prior to departure is the airline’s responsibility. Unfortunately, there are many companies that offer such services at LHR, and so there is no central control of all the aircraft de-icing resources. However this is something HAL are working on. Varying levels of SLAs between the companies and airlines mean that sometimes a crew will be called away from de-icing one aircraft from airline A to de-ice and aircraft from airline B because they offer B the gold service and A only the silver service. By the time they are finished with B, they need to start again from scratch on A.
There are remote de-icing areas for aircraft, as KARFA has pointed out, and these are used. No, there is not enough space for permanent de-icing pads at the moment, without a significant impact on operations the other 360 days of the year.
Anti-icing and De-icing of runways and taxiways is HAL’s responsibility. They have all the equipment, and personnel, that you’d expect. However, and this is where LHR is unique, there is no way any Airport that is scheduled to 99.5% capacity can cope with one runway being closed for 20 minutes for snow clearing, before closing the other one for 20mins. LHR is so space constrained the issue very quickly becomes where to locate all the snow you have cleared off the runway and taxiway. It can’t be left by the side of the runway, as it would very soon create an obstacle for the engines and wings of aircraft.
Comparisons are often made to other airports that cope much better. Yes. Of course they do. They don’t have 0.5% spare capacity, and most likely have far more snow days over a far longer period. Airlines don’t want HAL to keep trained, qualified teams of people just waiting for that phone call without having other jobs at the airport. Hundreds of people employed just on the chance that there might be snow at LHR? No chance. That’s what happens at airports like Calgary, Toronto and in Scandinavia, the workers who during the summer maintain the airport’s taxiways and lighting systems and perform myriad other activities, can’t do that work in the winter, and so the airport has a ready pool of trained manpower, and they all know that there will be snow/ice conditions from late October to February every year.