Obydwie są poprawne. Taka jest ogólna zasada. W BrE nie wymawia się "r" na końcu słowa lub w formie końcówki "re", jeżeli kolejne słowo zaczyna się na spółgłoskę. Jeśli zaś na samogłoskę to "r" się wymawia.
It's safe to say that, when learning British English, the "r" should not normally be pronounced EXCEPT when the following word starts with a vowel, where it always should. The letter "y" very rarely acts as a vowel at the start of words in English so normally the "r" would not normally be sounded. For example in "That is their yatch" you wouldn't sound the "r".
Most British speakers combine words in phrases like "there is" into a single continuous sound and the r is sounded for convenience.
...some British accents (Scottish, Lancashire, Cornish etc) pronounce "r"s at the end of words - like in American English - but these are regional differences that I wouldn't worry about when learning English!