Pronunciation of words like thanks, land, and

A merger of the phoneme /æ/ with /ɛ/ is uncommon in native English accents. That is, it is rare for a single speaker to pronounce "land" and "lend" the same way. There is a lot of phonetic variation in this sound, though: one speaker's "land" might sound like "lend" to a speaker of another variety of English.

Beyond this, for many speakers of North American English, the phoneme /æ/ is pronounced in different ways depending on the following consonant. It's generally raised, or brought more in the direction of [ɛ], before the nasal consonants /m/ and /n/. It is also generally raised to a lesser degree (as well as lengthened) before voiced non-nasal consonants. Its treatment before other consonants, /ŋ/ in particular, varies considerably depending on the dialect.

(Labov, 2006)

(I got much of this information and the chart from a discussion on the Wordreference forums that might be worth a look-over.)

In British English, I've never heard of /æ/ raising being common before nasal consonants. British English varieties are more likely to have the trap-bath split, which involves a backing and lengthening of /æ/ to /ɑː/ in some words in various phonetic contexts, including /ænt/~/ɑːnt/, /antʃ/~/ɑːntʃ/ and /æns/~/ɑːns/.