The section of RSGB bandplan you quoted gives exactly two USB frequencies within the WRC15/UK overlapping allocations, one at 5.354 MHz and one at 5.363 MHz. The old “UK 60m BAND UTILIZATION CHART” displayed things a bit more clearly, but only gave a single USB frequency within the overlap zone. I figure that 5.354 MHz is probably the only sensible USB frequecy that fits both with WRC15 and with UK at present.