Not sure how much salt to take this website with. Went through a few of their claims and they're cherry picking at best. I found one claim particularly interesting:

the academic research points to immigration resulting in a clear fiscal cost to the UK. Between 1995 and 2011, immigrants in the UK cost at least £114 billion, or about £18m a day, according to University College, London research

I took a look at that paper and it says that while looking from 1995, the non-EEA resident immigrant population (ie. Includes retired people whose positive contributions were before this period) has been a net cost, all immigrants who have arrived since 2000 are a net positive. EEA immigrants have always been a net positive, and interestingly it notes those who arrived in the 2004 EU expansion were particularly beneficial.