1) There are less that 300 irregular verbs.
2) Most irregular verbs change the vowel of the base to make their past or -ed participle forms. This is called vowel gradation. For example:
meet-met / take-took / speak-spoken
3) The -ed ending is never used in a regular way with an irregular verb. It is often not used at all - won, met, cut, sat - An important pattern with some verbs is the use of a variant form, in which the 'd' sound of the ending changes to a 't'. For example:
burned - burnt / spilled - spilt / kneeled - knelt.
4) Burned is more common in American English than British English. The 'd' and 't' forms do not convey the same thing. The 'd' form emphasises the duration of an action - it burned for weeks. Whereas the 't' form would be more appropriately used when saying - ow, that burnt me.
5) There are seven classes of irregular verb:
a) There are about 20 verbs whose only irregular feature is the ending used for both past and -ed participle forms: have - had / send - sent / burn - burnt - burned.
b) There are about 10 verbs whose past tense is regular, but their -ed participle has an -n ending and a variant form in -ed: mow - mown - mowed / swell - swollen - swelled.
c) There are about 40 verbs that have the same ending for both the past and -ed participle forms, but they are irregular because the vowel of the base form changes: keep - kept / sleep - slept / teach - taught / sell - sold.
d) There are about 75 verbs that have an -n ending for the -ed participle form and an irregular past form. The vowel of the base also changes: blow - blew - blown / take - took - taken / see - saw - seen / undo - undid - undone.
e) There are about 40 verbs that have the same form throughout: cut / let / shut / broadcast / outbid.
f) There are about 70 verbs that have no ending for both past tense and the -ed participle. The vowel used in the base changes: spin - spun / mislead - misled / sit - sat / stand - stood.
g) There are about 25 verbs that have no ending, the past and -ed participle forms are different, and the vowels change with each form: swim - swam - swum / begin - began - begun / go - went - gone.