The direction and speed of the tidal stream varies with height of tide, and can be found for each hour before or after high water at the Standard Port. A spring tide has a speed about double that of a neap tide.
If in between springs and neaps, for maximum accuracy you have to interpolate between the spring rate and the neap rate.
Reeds Almanac: Page 62 (Year 2020):
Computation of rates table to find out the exact range.