permanent job -going on holiday

I start a job as a health support worker on wards which is listed as permanent. I do the job from now up until July. I know that i will be going on holiday in July for 4 weeks but I won't tell them this now since I would still be new and it is not a good first impression. Providing I give them at least a month/ a month and a half's notice can I do that or will they sack me. I would have liked to go on holiday, come back and do the job until September. Do you reckon they would allow that or will I just be sacked when /i tell them /i cannot come in because I am on holiday. In which case I will just be better off resigning around June time and not going back. However this looks bad if I need them for refree purpises. Alternatively could I take no holidays at all and work during any holidays then just save the holidays up for July- I'm not sure how all this works