UK Biobank is a major prospective epidemiological study that is carrying out detailed multimodal brain imaging on 100,000 participants, and includes genetics and ongoing health outcomes. We present a new open resource of GWAS summary statistics, resulting from a greatly expanded set of genetic associations with brain phenotypes, using the 2020 UK Biobank imaging data release of approximately 40,000 subjects, 3,000 phenotypes, and 10 million variants with MAF greater than 1 percent. We include associations on the X chromosome, and several new classes of image-derived phenotypes (primarily, more fine-grained subcortical volumes, and cortical grey-white intensity contrast). We develop a method to identify clusters of associations across phenotypes (Peaks) and we find 692 replicating clusters of associations, including 12 on the X chromosome. Our novel associations implicate pathways involved in the rare X-linked syndrome STAR (syndactyly, telecanthus and anogenital and renal malformations), Alzheimer's disease and mitochondrial disorders.