The geographic factor that made it unlikely that World War I battles would be fought in Great Britain is the English Channel, which separates Great Britain from the rest of Europe.
The channel has always been the best defense of Great Britain, as it has allowed it to intervene on one side and on the other to avoid possible threats in European conflicts. For example, it prevented Napoleon and Hitler from invading the country.
The English Channel works as a water barrier of at least 34 km away (its maximum is of 250 km), which makes a land invasion impossible.
