While these curricula may be a useful way of structuring education around your faith, you cannot rely on them being accepted as alternatives to GCSEs or A-levels in the UK. ICCE is accepted as an 'overseas qualification' meeting the maths and English criteria for 16-19 education, so if you hold this certificate you should not have to continue studying maths and English at college. However, we can't say that they are more generally recognised. Some colleges will accept the ICCE General Certificate as an alternative to GCSEs, while others will not.
Some teenagers have found that they needed to complete GCSEs in addition to the ICCE, in order to be accepted onto Level 3 courses. Some have found that the ICCE was not counted at GCSE level by universities which specified a minimum GCSE tariff in addition to A-levels.
There is also an ICCE Advanced Certificate which is described as an alternative to A-levels. A few UK universities have accepted students with only this qualification, but many others have stated that they would not do so.
Please ask on the Home Education UK Exams & Alternatives Facebook group or the HE Exams Yahoo group for recent experiences from home educators if you are considering these routes, and most importantly, check direct with any university or college you are considering applying to.