Because both the futures and spot are based upon the same base currency, GBP. Thus any movement in them is going to be equivalent (on an intraday basis). The same holds true for AUD futures and EUR futures.
CAD, CHF, JPY - they all trade on the spot markets with the USD as the base currency. Thus, the tick size will vary depending upon the exchange rate. Conversely, the CAD, CHF, and JPY futures all use the foreign currency as the base, meaning the tick size is static and will not mirror the tick size of the spot trade.