Hi
You can pay monthly; this is for UK + Worldwide info:
From "Different Membership packages offered by Ancestry .co .uk"
"Essentials Membership contains all the essential UK records needed to start researching your family history - such as Birth, Marriage & Death Indexes and Census records. It costs £83.40 a year, or, if you are a monthly member, £10.95 a month.
Premium Membership contains all of the above, but also includes UK records that predate civil registration (1837), such as Parish & Probate records. It costs £107.40 a year, or, if you are a monthly member, £12.95 a month.
Worldwide Membership, you get all the benefits of Premium, as well as access to Ancestry's global record collection - featuring records from USA, Canada, Australia and more. You can also access our Irish record collection. World membership costs £155.40 a year, or, if you are a monthly member, £18.95 a month. "
Kind regards
Gaie