I am a great fan of John Taylor's books, Greek to GCSE 1&2 are outstanding books and if, as an adult or younger student, you want to read the classics or the New Testament in the original, they are a great starting point.
Greek Beyond GCSE (2008), ISBN 978 1 85399 704 4, does indeed take you up to AS level classical Greek, but vocabulary tops out at only 830 words, so you will need to get something like Jerry Toner's 'Greek Key Words' (top 2000 most common words) to build vocab quickly, or if you are a New Testament reader, the old but good 'Pocket Lexicon of the Greek New Testament' by Souter. And a lexicon like the famed Liddell & Scott (abridged) - the old 1949 hardback impression is excellent quality print if you can get it - or the new 'Pocket Oxford Classical Greek Dictionary' by James Morwood & John Taylor (again!)
Warning - none of John Taylor's books have an answer key as they are school texts. Self-teach will be tough going. Or find a course such as the Open University (which I did) - or get a correspondence course of some type (cheaper, pace yourself). These books are great additives.
This current book continues the high quality set by Greek2GCSE1&2 and exceeds it. Struggling with the optative? - read the seven line explanation at the foot of page 12. Need a quick overview of subordination in complex sentences (the typical Greek sentence)? - see pages 44 and 45.
CONTENTS (the entertaining translation passages in chapters one to four I omit)
Glossary of grammar terms
Chapter 1: direct and indirect questions, correlatives, subjunctive and jussive, deliberative questions, optative, wishes, conditional sentences, potential optative/indicative with 'an'
Chapter 2: perfect tense, pluperfect tense, deponent verbs like perfect middle, numerals, prepositions, compound verbs, omicron contraction verbs, subordination and the complex sentence, useful idioms
Chapter 3: verbs in -mi, verb 'isteemi', time clauses, more middles, verbs with dependent participle, verbs of fearing, nouns/adj. with epsilon contraction, privative alpha and compound adj.
Chapter 4: impersonal verbs, accusative absolute, complex relative clauses, articular infinitive/gerund, indefinite construction, verbal adj./gerundive, dual forms, crasis and elision, third person imperative, subordinate (esp. conditional) clauses in indirect speech.
Chapter 5: readings (37 pages): Xenophon, 'Anabasis' and 'Cyropaedia'; Lysias court speech 'On the murder of Erastosthenes'; Thucidides 'Curse of Cylon'; Demosthenes 'Conon and his Gang'; Plato 'Protagoras', and 'Lost Atlantis' in the 'Timaeus'; Plutarch on Sparta; Lucian's 'Anacharsis'
Chapter 6: summary of syntax and Reference Grammar
Appendices: 1 - words easily confused, 2 - Greek and Latin constructions compared
Vocabulary - Greek to English, English to Greek
Index