Yes you need to go back and work for more than 26 weeks, I had the same problem 4 years ago after working overseas for a year. I only got SMP the for duration of my maternity leave. All your previous service is cancelled out. If possible hang out for that period of time, as the
maternity pay is good, (experienced this the 2nd time around) generally 1/2 pay plus SMP for the first 5 ...